I have a specific project with the following needs :
parameter which set range in the schedule in which events can be created (it implies : lock the “opposite” range to avoid events). For instance, I would like to authorize events between 8:00 to 12:00 for monday to friday. I would like to be able to set any kind of range easily.
parameter which set specific time for events. For instance, each event would last 30 minutes.
That depends a lot whether you want this only for the Nextcloud calendar app or for any CalDAV client that connects to Nextcloud. If you only want it in the Nextcloud calendar app, probably 20 to 30 hours of work, more if the developer has to familiarize themselves with the code first.