When i turn my engine off the turbo timer keeps it running for usually 10-20 seconds, i thought it'd be longer?

I know it depends on how it's been driven etc, but is there a general rule of thumb for how long you should keep the car running after a drive to let the turbo cool down?

Ta.

 

I drive off boost for about 2 miles away from home and when stopped leave to tic-over for 1min before turning off

 

I usually let mine take care of it's self on auto,but as above the last part of my journey home is off boost due to speed limits mainly.

On reaching home if the time is quite low I whack it onto 3 mins anyway.

 

How do you know if your car is 'off boost'?

Sorry to sound stupid, but im new to turbos lol.

 

Drive it using low revs so the turbo doesn't spin up