It's the same as the mana perception timer, which is on the order of 2.5-3.5 minutes (3.5 is basically the time between experience pulses). The only timer that's different for PH is the cooldown timer as you move from room to room. PERCEIVE (mana levels) doesn't have one (or else it's less than the RT and thus you never bump into it), PERCEIVE HEALTH has you wait something like 15 seconds.

J'Lo, I'm a ranger.. I'd believe anything.....
The Manipulation List -- http://symphaena.com/index.html