I'd QT first, but if you're not going to........ Float the bag for about 15 minutes to temp acclimate, then dump the bag of water & fish into a clean 5gal bucket & run a piece of air tubing from the tank to the bucket with a few knots tied in for drip adjustment. Each time the water volume doubles, take a cup & remove half (do this a few times). Agree on the hour to hour & half.
Wanna calculate the cost of that new reef tank?? Take your worst nightmare, double it, and you're halfway there.