I thought the idea of the turbo timer wasn't to let the oil cool per se, it was to let the oil keep flowing (while the engine is running) through the turbos to cool them. When you turn off the engine, the oil stops flowing and that's when the turbo seals can crack.
Anyhoo, if I need to let the turbos cool I do one of the following:
1. (if servo is busy), just line up behind someone that is filling up. Waiting for them to do their thing is usually long enough.
2. (if servo is empty), just line my car up with the pump and wait the required time, then turn it off.