diff --git a/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/OnlyIfNoUsers.php b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/OnlyIfNoUsers.php
new file mode 100644
index 0000000000..746fa83a86
--- /dev/null
+++ b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/OnlyIfNoUsers.php
@@ -0,0 +1,55 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM – Open Source CRM application.
+ * Copyright (C) 2014-2026 EspoCRM, Inc.
+ * Website: https://www.espocrm.com
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU Affero General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU Affero General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Classes\FieldValidators\WorkingTimeRange\Calendars;
+
+use Espo\Core\FieldValidation\Validator;
+use Espo\Core\FieldValidation\Validator\Data;
+use Espo\Core\FieldValidation\Validator\Failure;
+use Espo\Entities\WorkingTimeRange;
+use Espo\ORM\Entity;
+
+/**
+ * @implements Validator<WorkingTimeRange>
+ */
+class OnlyIfNoUsers implements Validator
+{
+    public function validate(Entity $entity, string $field, Data $data): ?Failure
+    {
+        if ($entity->getCalendars()->getCount() === 0) {
+            return null;
+        }
+
+        if ($entity->getUsers()->getCount() === 0) {
+            return null;
+        }
+
+        return Failure::create();
+    }
+}
diff --git a/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/RequiredIfNoUsers.php b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/RequiredIfNoUsers.php
new file mode 100644
index 0000000000..7730b09450
--- /dev/null
+++ b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Calendars/RequiredIfNoUsers.php
@@ -0,0 +1,52 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM – Open Source CRM application.
+ * Copyright (C) 2014-2026 EspoCRM, Inc.
+ * Website: https://www.espocrm.com
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU Affero General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU Affero General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Classes\FieldValidators\WorkingTimeRange\Calendars;
+
+use Espo\Core\FieldValidation\Validator;
+use Espo\Core\FieldValidation\Validator\Data;
+use Espo\Core\FieldValidation\Validator\Failure;
+use Espo\Entities\WorkingTimeRange;
+use Espo\ORM\Entity;
+
+/**
+ * @implements Validator<WorkingTimeRange>
+ */
+class RequiredIfNoUsers implements Validator
+{
+
+    public function validate(Entity $entity, string $field, Data $data): ?Failure
+    {
+        if ($entity->getCalendars()->getCount() !== 0 || $entity->getUsers()->getCount() !== 0) {
+            return null;
+        }
+
+        return Failure::create();
+    }
+}
diff --git a/application/Espo/Classes/FieldValidators/WorkingTimeRange/Users/OnlyIfNoCalendars.php b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Users/OnlyIfNoCalendars.php
new file mode 100644
index 0000000000..24c82a5a3c
--- /dev/null
+++ b/application/Espo/Classes/FieldValidators/WorkingTimeRange/Users/OnlyIfNoCalendars.php
@@ -0,0 +1,55 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM – Open Source CRM application.
+ * Copyright (C) 2014-2026 EspoCRM, Inc.
+ * Website: https://www.espocrm.com
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU Affero General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU Affero General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Classes\FieldValidators\WorkingTimeRange\Users;
+
+use Espo\Core\FieldValidation\Validator;
+use Espo\Core\FieldValidation\Validator\Data;
+use Espo\Core\FieldValidation\Validator\Failure;
+use Espo\Entities\WorkingTimeRange;
+use Espo\ORM\Entity;
+
+/**
+ * @implements Validator<WorkingTimeRange>
+ */
+class OnlyIfNoCalendars implements Validator
+{
+    public function validate(Entity $entity, string $field, Data $data): ?Failure
+    {
+        if ($entity->getUsers()->getCount() === 0) {
+            return null;
+        }
+
+        if ($entity->getCalendars()->getCount() === 0) {
+            return null;
+        }
+
+        return Failure::create();
+    }
+}
diff --git a/application/Espo/Entities/WorkingTimeRange.php b/application/Espo/Entities/WorkingTimeRange.php
index 282842520c..08ba264e75 100644
--- a/application/Espo/Entities/WorkingTimeRange.php
+++ b/application/Espo/Entities/WorkingTimeRange.php
@@ -128,4 +128,13 @@ class WorkingTimeRange extends Entity
         /** @var LinkMultiple */
         return $this->getValueObject('users');
     }
+
+    /**
+     * @since 9.3.1
+     */
+    public function getCalendars(): LinkMultiple
+    {
+        /** @var LinkMultiple */
+        return $this->getValueObject('calendars');
+    }
 }
diff --git a/application/Espo/Resources/layouts/WorkingTimeRange/detail.json b/application/Espo/Resources/layouts/WorkingTimeRange/detail.json
index ccfc2151eb..67a59492b4 100644
--- a/application/Espo/Resources/layouts/WorkingTimeRange/detail.json
+++ b/application/Espo/Resources/layouts/WorkingTimeRange/detail.json
@@ -13,9 +13,13 @@
                 {"name": "timeRanges"},
                 false
             ],
+            [
+                {"name": "users"},
+                false
+            ],
             [
                 {"name": "calendars"},
-                {"name": "users"}
+                false
             ],
             [
                 {"name": "description"}
diff --git a/application/Espo/Resources/layouts/WorkingTimeRange/detailSmall.json b/application/Espo/Resources/layouts/WorkingTimeRange/detailSmall.json
index ccfc2151eb..67a59492b4 100644
--- a/application/Espo/Resources/layouts/WorkingTimeRange/detailSmall.json
+++ b/application/Espo/Resources/layouts/WorkingTimeRange/detailSmall.json
@@ -13,9 +13,13 @@
                 {"name": "timeRanges"},
                 false
             ],
+            [
+                {"name": "users"},
+                false
+            ],
             [
                 {"name": "calendars"},
-                {"name": "users"}
+                false
             ],
             [
                 {"name": "description"}
diff --git a/application/Espo/Resources/metadata/entityDefs/WorkingTimeRange.json b/application/Espo/Resources/metadata/entityDefs/WorkingTimeRange.json
index 3a89ba0bf3..80d9090ffe 100644
--- a/application/Espo/Resources/metadata/entityDefs/WorkingTimeRange.json
+++ b/application/Espo/Resources/metadata/entityDefs/WorkingTimeRange.json
@@ -34,12 +34,20 @@
         },
         "calendars": {
             "type": "linkMultiple",
-            "tooltip": true
+            "tooltip": true,
+            "validatorClassNameList": [
+                "Espo\\Classes\\FieldValidators\\WorkingTimeRange\\Calendars\\OnlyIfNoUsers",
+                "Espo\\Classes\\FieldValidators\\WorkingTimeRange\\Calendars\\RequiredIfNoUsers"
+            ],
+            "autocompleteOnEmpty": true
         },
         "users": {
             "type": "linkMultiple",
             "view": "views/working-time-range/fields/users",
-            "tooltip": true
+            "tooltip": true,
+            "validatorClassNameList": [
+                "Espo\\Classes\\FieldValidators\\WorkingTimeRange\\Users\\OnlyIfNoCalendars"
+            ]
         },
         "createdAt": {
             "type": "datetime",
diff --git a/application/Espo/Resources/metadata/logicDefs/WorkingTimeRange.json b/application/Espo/Resources/metadata/logicDefs/WorkingTimeRange.json
index 605b9f7262..3684ab3489 100644
--- a/application/Espo/Resources/metadata/logicDefs/WorkingTimeRange.json
+++ b/application/Espo/Resources/metadata/logicDefs/WorkingTimeRange.json
@@ -11,7 +11,7 @@
                 ]
             }
         },
-        "users": {
+        "calendars": {
             "visible": {
                 "conditionGroup": [
                     {
@@ -19,8 +19,36 @@
                         "value": [
                             {
                                 "type": "isNotEmpty",
-                                "attribute": "id"
+                                "attribute": "calendarsIds"
                             },
+                            {
+                                "type": "isEmpty",
+                                "attribute": "usersIds"
+                            }
+                        ]
+                    }
+                ]
+            }
+        },
+        "users": {
+            "required": {
+                "conditionGroup": [
+                    {
+                        "type": "or",
+                        "value": [
+                            {
+                                "type": "isEmpty",
+                                "attribute": "calendarsIds"
+                            }
+                        ]
+                    }
+                ]
+            },
+            "visible": {
+                "conditionGroup": [
+                    {
+                        "type": "or",
+                        "value": [
                             {
                                 "type": "isNotEmpty",
                                 "attribute": "usersIds"