There seems to be a bug when switching from Business hours to appointments. When creating a new location and switching to appointments you can only add appointments to the former set business hours. However the Business hours tab is removed and switches to pickup appointments when selecting Enable Pickup Appointments under Name & type.
If you remove all Business hours before switching type, you can’t add anything to the Pickup appointments calendar as it is all greyed out without any pluses.
A workaround was to first set business house on all days, then switch to appointment type. Open appointments calendar and remove all times. Then you get a plus sign so you can add irregular times.
Would be nice if you could have no business hours from start and the pluses would show in appointment calendar.