This is what you do. I have used this tactic before in an emergency situation.
Find a hotel... in the morning at/around checkout time or so, housekeeping usually open the doors to a bunch of rooms. Find one with no maid in it (usually, there will be like 5-10 open at a time, maybe an entire floor... maybe only 2 or 3, but figure it out) go in that room, find the do-not-disturb tag, and hang it on the door if you can. Lock it.
If the room has bags and stuff in it (AKA: it's being occupied by someone, or some folks who are out doing their daily bullshit), then you're basically in the clear. You can take as long a shower as you want, and you're fucking golden. You can probably watch some TV too, and just hang out and relax (raid the mini-bar I suppose, if you feel like being a dick or you're going hungry)
If the room's not occupied (much more likely the case) then you have maybe 2-5 minutes to take a shower before a maid comes in and realizes you're there. If a maid comes and knocks on your bathroom, say something to the extent that "I'M A GUEST HERE, THERE SHOULD HAVE BEEN A DO-NOT-DISTURB TAG ON THE DOOR! PLEASE COME BACK LATER" or anything of that sort in an annoyed tone. This will at least confuse the maid and buy you more time to finish up and leave before she finds out the room wasn't occupied after all...
and voila... you just stole a fucking shower.
Have a nice day, Bluename.