The game randomly determines what action the merc uses when engaging a monster. One of the possible actions is turning on his aura. In effect, how long it takes him to turn on his aura is completely random.
The level at which you hire a merc doesn't matter, but the difficulty you hire him in does. Mercs hired in lower difficulties will have slightly better stats.
Last edited by muzzz; 30-11-2007 at 14:02.
Reason: clarified two sentences