Several hours in a bag isn't bad, as long as they have been bagged properly. This means not overstocking the bag, 1/3 water, 2/3 air, and having been fasted for 24 hours before bagging. Unless the water in the bag is very soft you should not see much of a pH drop.
When I get fish shipped in first thing I do is open the bag and immediately add a double dose of dechlorinator that neutralizes ammonia. This is the biggest concern with fish that have been shipped, many having been in the bag 24 hours give or take. For drip acclimating I try to double the water volume every hour, for about 3 hours. If the fish look distressed slow the drip rate, if they seem to pick up with the fresh water increase it.
After 3 hours they should have about 87.5% tank water, now it's time to take the average couple of fish, add them to the tank, and observe for about 10 minutes. If the sample fish in the tank seem ok, add the rest of the fish. If they don't, leave them be, drip the fish in the bag for another hour.
Do not add the bag water to the tank, net out the fish, or pour the fish into a net held over a bucket. Leave the lights off for 24 hours, light the tank with only room light. Angels should be fine with not being fed the first 24 hours, some species, generally wild caught, you do want to get them to eat as soon as possible. This is where live food or fresh vegatables are an advantage.
I buy & sell fish at local & not so local auctions on a regular basis, the water in the Midwest is generally hard to very hard, pH 7.2-8.0. These fish can be acclimated faster than 3 hours most of the time. I get fish shipped in from South America on occasion, wilds that are shipped in the local very soft water with a lower pH. Some of these are fine with a faster acclimation, many take longer than 3 hours.