Timing is iffy, at best. You cannot get consistent results even if you time the cooking process with split-second accuracy - several influential variables exist. The tap water temperature usually varies according to the outdoor temperature and time of day by as much as 15F. Even if you use the same pan, the quantity of water you put in it will vary daily unless you measure the volume carefully. Finally your range probably doesn't have the precision controls that would allow you to set the same exact cooking temperature each day.
** Asian Recipes