If you set the turbo timer for like 10 seconds, the turbo will still spool for 10 seconds after the engine is off iirc...
A turbo timer leaves the engine running for X amount of time after turning the ignition off. Supposedly to cool it all down. They're a gimmick, just drive slowly 5/10 minutes before turning your car off, who ever heard of sitting still with an engine running cooling it down?