There is no particular reason it should be 2 minutes. Certainly not for both jaws, if you took 2 minutes per jaw that would be more reasonable.
The point of this timer is probably (I don't know that for a fact) to push most people to brush much longer than they would as most people still brush for only 30-45 seconds a day.
The point of this timer is probably (I don't know that for a fact) to push most people to brush much longer than they would as most people still brush for only 30-45 seconds a day.