I have to make a 12x18 sheet cake to be delivered on Saturday morning. I wanted to bake and crumb coat the cake late Thursday afternoon, and decorate the cake Friday. My freezer is too small for the cake to fit. I was wondering would it be okay to leave the cake out overnight if I wrap the crumb coated cake really well with plastic wrap?

yes

Sure.  No problem as long as it is well crumb coated.

Yes you can. I used to do that before when my freezer was too small to fit the cake. I just made sure to securely wrap plastic around it and it's always fine in the morning.

Thanks guys!

To clarify, if there is any sort of filling that needs to be refrigerated, the answer is no.  I know I'm in the minority for filling even a sheet cake, but thought I'd throw it out there.

Also, if you are crumb coating it with frosting that needs refrigeration, say like a cream cheese based frosting, it does need to be refrigerated.  I would stick with something like an American Buttercream if you need to leave it out.

Good luck with your cake!