schedule template: allow to specify "whole day" / allow more then 8 hours for a single appointment

[steadfasterX]

I would like to see an option to block a whole day.
it would be enough (for my use cases) to give the possibility to modify the max duration for an appointment in the scheduler. that is currently set to max 8 hours which is not the whole day (we start at 8am and end 8pm) so it would be great to specify the max hours.

I hope that might be a quick change?

parts of it are maybe related to: #549 while the use case there is a bit different.