I personally use the float acclimation and add water to match salinity method. Most often than not the water in the bag is significantly lower than that of my tank and I don't want to risk the critter experiencing salinity shock. I like to pour out about half of the bag water and then place the bag in my tank. After about 15 minutes I add about a 1/2 cup of tank water and repeat that every 15 minutes taking water out as necessary to avoid any bag water from over flowing into my tank. This usually takes about an hour or so.

What works for you?