As with any additive, you want to ensure even distribution. This is why you ripen, to let the bacteria wake up and disperse through the milk from their concentrated form. This is why you dilute concentrated solutions of CaCl2, annato, and rennet. This is also why you stir up and down for liquids, such as CaCl2 solution, rennet, and annato. Same thing applies to lipase. You want it close to the fat molecules, meaning you want it distributed throughout the milk. Adding it first is a great idea. Adding it with culture is also a great idea. Adding it right before rennetting is a bad idea. Adding it and not stirring is also a bad idea. Adding it, stirring briefly, and letting the lipase float on top is sort of in the middle, because eventually it will dissolve.
So the underlying principle is distribution. Any practice you use to ensure even distribution is fine. Distribution becomes a bigger issue especially with larger vats.
Personally, I add either before or with culture when using DVI, and before when using bulk/mother starter.