Actually, the 'correct' procedure is cumbersome.
On a more risky basis, the caretakers are often willing to let out rooms after about 1900 hrs, when they are reasonably sure that no one with a booking is likely to show up. Sometimes, it is conditional: that if an advance booking person turns up, you'll have to vacate!
Usually, there is no problem. Whenever a booking is made, miles away in the relevant city, the caretaker is sent intimation. He is almost always aware of the bookings status.
And, a good T.I.P. (To Insure Promptness) goes a long way with these poor fellows!
What works best is a wee bit of alcoholic beverage!