I agree with Farm Girl 1.I've always kept mine open even at that age. They didn't sleep in them or anything they just explored them. So I'd say its fine to open them.
I agree with Farm Girl 1.
I have only my current gals, but never had to close the nests. All who showed early interest and played in and explored them started laying there. The one who showed no early interest was initially a floor layer.
I would leave them open, unless they try to sleep there.
If you decide to close them, I would reopen when the pullets are showing signs of maturity.