I know I can switch off auto-lock altogether, but actually I just want to prevent the screen from being locked when I am playing games.
If the game maker didn't program the screen to not lock, you have to use Apple’s switch for the entire system. It's hard to imagine many games where you don't touch the screen once every 5 minutes, but if so, request the game developer to add a switch or setting at overrides the system default for their game.
Settings App > General > Auto Lock
Then you can choose between
- 1 Minute - 2 Minutes - 3 Minutes - 4 Minutes - 5 Minutes - Never