Good question, but no. Not all of the bats leave at the same time. They go out in groups and shifts, and return back and forth all night. At no time is 100% of the colony out at once. So if you seal at night, you will be sealing some bats in your home. This could cause them to die or worse, force them into the living space of your home. You need to use proper bat removal and bat exclusion methods to keep this from happening.