We just started the alarm with DS3 (5.5). I would not normally have done it this early as DS2 outgrew it on his own around this age, but we suspected that his night waking was related to it, he was soaking through regular pull-up so we were moving to GoodNites or Underjams ($$) and we already had the alarm from DS1.

It only took him about a week of the alarm going off 1-2x per night and the last three nights have been dry. Hoping this is a trend!

DS1 took fully 6-8 weeks of waking to get through it. We saw steady progress in that time, going from 3-4 wakings to 1-2 and then down to 1, but it was a looooog time.