You can use eventDrop callback calling revertFunc if the event is moved to a wrong range (https://fullcalendar.io/docs/event_ui/eventDrop/)
@cptx032 Thanks for your help. Could I have a solution better than this? I mean that some technic fullcalendar configuration.
In combination with @cptx032's answer you can use businessHours to grey out the specific area as you can see here
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In combination with @cptx032's answer you can use businessHours to grey out the specific area as you can see here