when the tree starts counting down from double yellows, to the final yellow, as soon as the final yellow hits, start going...may take a little work to get your timing down, but you want you reaction time as close to .000 as possible, generally .100-.300 is pretty darn good. this will help you get good 60' times. reducing your 60' times every 1/10th of a second, helps you bring your ET's down 2/10th's of a second.
good luck and have fun.