back:
The phrase at the back of can mean two things: The most common is in reference to time, where the back of an hour is the period just after it. “Ah’m meeting them at the back of four.” There is no set length to this period but it would probably not extend past twenty minutes: “Ye were meant to be here at the back of nine and it’s half-nine already.”
The other use is to mean behind: “She left her motor at the back of Woolies.”