The load up time is more accurate and also helps on adjusting the idle better.

Warm up the engine,make a full throttle run to clear the engine and bring it to idle.Let it sit there and hear the revs.They should drop slightly at around 10sec.Any sooner and it's too rich, later means it's lean.You can adjust according to the track you race up to 15sec load up.Not more.It will heat up the engine especially on a tight track.