Hi! I’ll ask the team to look into the possibility of delaying the calculation time (maybe offer an option to set a custom duration), but I also wanna understand your use case some more.
What’s the registration form like? The “class” is a linked records field, right? Can’t you just run a validation condition against a rollup field to check if the class is full?
Also, why a “full class” is showing as an option in the first place? Shouldn’t you hide it by filtering out any class where students = 20?