Question about how long can a hotel wait after checkout to charge your credit card?

My wife bought a night at a hotel online prepaid. We booked it then decided to stay another night and reserved the second night. When we arrived, they took our credit card number and our prepaid printout for the one night and we gave a $100.00 deposit for incidentals.When we checked out, we got our deposit back and checked out. My question is, its been 8 days since we checked out and our account hasn't been charged yet. How long do they have to charge us. We live payday to payday like most people and trying to remember that that money needs to be there is worrisome. Also, I know there are taxes involved also, but the hotel never specified verbally or on paper how much.