Drip acclimation can be very hard on fish. I don't even bother with it anymore unless it is a sensitive saltwater creature and even then it is done with great care. When the bag is closed up at the store pH starts to drop and ammonia levels, of course, rise. The higher ammonia is ok for a time as the lowering pH works to keep it in a 'not so toxic' form. When you open the bag at home pH suddenly begins to increase. Because of the increase in pH the ammonia is quickly transformed into a very toxic substance. A slow drip does nothing to combat this effect and the fish end up damaged from ammonia poisoning.
In short, don't bother with drip acclimation. Just float the closed bag for fifteen minutes to match temp and then open and add a half cup of tank water to the bag every ten minutes for an hour. When the water in the bag has doubled, or you hit the 30 minute mark, dump half out and continue.