How long should I wait for the crumb coat to dry, before I can finish to cover the cake?
Mine usually takes 15 mins, but I have had some take an hour depending on the humidity and warmth of the kitchen.
When it is applies thin enough you don't have to wait long at all = like just a few minutes.
I usually put the finishing coat on right away. I don't wait for a crumbcoat to crust.
I would wait about 10 minutes. As long as it's somewhat crusted over it will help to hold your crumbs in and that's all you need!