It seems the AI is capable of firing lock on missiles the moment it is facing its target, normally this would require a few seconds.
How to reproduce:
# make a ship with lock on missile (missile + beam), get in a ship yourself and enable god mode
# spawn 5-10 of those as AI mobs, use a radar jammer yourself to experiment with their reaction timing
# you'll notice that often after disabling your radarjammer, they will instantly fire lock on missiles at you -> they don't have a lock on timer.