lowandslow is partially right. In the NHRA, the time is started when the light goes green and the R/T is taken into consideration on the final 1/4 mile time.
By the same token, most tracks have the time start when your wheels leave the start line (as in my case.. you can look at the bottom of my slip and it says "AUTOSTART: OFF". If it were ON, the R/T would be considered. Just to prove my point, check this video of the Titan Supra. The driver has a horrible R/T (of more then 1 sec.) but still has a time of 8.9. If his R/T mattered, the time would be over 10 seconds. Check the vid yourself:
http://highboost.com/movies/TitanRace/titan890a.mpeg
Either way, here's the time slip that you vultures have been waiting for. I am in the right lane.