I think you just add it at pitching to give it a longer residence time in the beer at warmer temps; fermentation is usually the warmest you're going to store any beer for a reasonable length of time. Usually, once fermentation is over, people will chill the beer, and transfer it to kegs then store it cold. The enzyme probably doesn't work well at fridge temps. If you're bottle conditioning, though, I bet you could add it at bottling and be fine.
I've used it 3-4 times with pale lagers, and been very impressed. It gives a really clear beer, as advertised, without chill haze (I've had problems with that in the past).