we use Picker's method and i have run test just for fun. 3 x 10 does not look the same as 30 sec. This is not to mean that one is better than the other ( i don't want to get into a P*****g contest over which system works).
My feeling is that timers may or maynot be completely accurate. Unless you take a stop watch in and check each timer who cares. Consistency is the important element. My students use the same work station to help control the variables and enhance the opportunity to maintain consistence work habits.