I've been looking at the rules for the combat phase and its steps, but I can't find this. It's clear when a creature becomes an attacking creature (when it's declared as attacking, created as attacking, or an effect otherwise says it is), but when does it stop?
I'd expect it to be either the beginning of the "end of combat step" or the end of the combat phase, but the distinction is important.
The situation that made me question this was, if you were playing as Oracle (Vanguard), could you use its ability to untap a creature after combat damage during the "end of combat step"? That would allow you to then use tap abilities (e.g. Llanowar Elves) or keep them as a blocker, effectively giving your creatures vigilance. This also goes for cards such as Maze of Ith, or even Kill Shot if you really wanted to kill a creature after letting it deal damage.