I typically try to get about 3-4 drips per second, let it drip for about 30 minutes, then dump half of the water and let it drip another 30 minutes. So a little over an hour for the whole process. Make sure you still float the bag to adjust it to the temperature of your tank. If you wanted to get fancy, you could get one of these:

http://socaltropicalfishoutlet.com/c...nk-p-1359.html