Suppose you have a template from 8 am to 5pm that every Monday that allows a particular group of users to make a booking. Suppose the resource it is applied to is also set up with a far term template beyond 7 days that denies all bookings to everybody, and a near term template at 4 days that opens up the time to allow anybody to make a booking.
Consider a researcher that wants to make a booking 6 weeks into the future at 1pm on a Monday. This researcher is waiting for the template to switch from the far term mode to the regular mode. When does this happen? Should the slot become bookable at 1pm, or should the whole 8am-5pm region become bookable at 8am on the day 6 weeks in advance? The former option is "rolling transition" and the latter is "instant transition".
