Hotels is something I know about. What Hotel? They all have specific late checkout times. For example Holiday inn is 2pm for priority club members. I can sometimes stretch it until 2:30 but the maids will yell and give me the stink-eye.
The Wynn in LAS was hardcore 12:00 noon. Wouldn't budge.
Nobody gives 3:30 The only way you can do it is if you check out ahead of time, but leave the door propped open and sneak back in.
It's not a matter of whether they have empty rooms. I causes them grief, because the maids have certain shifts.
Basically, you are looking for a free pressure washer.
Corporate will probably take it off your bill if you squeal loud enough, but are you in the right? No. Definitely not, unless they specifically told you late checkout was 4:00pm.
BTW- The Marriot rewards program sucks. Thats why I became a Priority Club Whore. I have something like 30 free stays accumulated, so I have that going for me.......which is nice.......