I agree with Fermion, cut a small hole to let it expand. I would also crack a window, compressed mattresses can smell a bit chemically at first

Also, can I unroll and let it do its thing on its frame or should it be on the floor?

Cant see how it would matter, but it would be preferable for me to get the frame setup and ready now and then deal with the mattress tomorrow if the plastic has to come off and I need the protector or if the plastic wont affect it decompressing then I can just do it all today and then take off plastic+do the protector tomorrow

If you cut a corner off the bag that should let air in while still keeping dirt/dust off. Then you can cut the rest of the bag off tomorrow.

That said, what are you worried about getting on your mattress over a single night? Do you have pets that will be checking it out?