[RWebb]

it makes a big difference whether it is a squirrel or a rat/mouse - the former are day active and latter night active

your wall is their lair and they will be in there when not active

if you close off their opening at the wrong time, they will die inside your house and stink (with some disease risk also) until the carcass dries out -- weeks or months

I would figure out the times they are inside & see what that tells you. You can do that while looking for the tiny entrance hole.

hope they don't have breeding nest in there, BTW