It should hold fuel pressure for a quite a bit. I admit, I've never really tested it longer than a minute or two, but on average, it drops about 10psi in 2 minutes and seems to stop.
Fuel is actually not supposed to drain back into the tank in modern vehicles, it's supposed to retain as much of it as possible. The one-way check valve prevents drain-back from occuring so that you can start it right up, the next time you go to start it. Also, to prevent vapor lock from occuring.
***Also, when you go to change the fuel pump, please be careful. I've seen too many accidents with fuel tanks, and it's not pretty. Make sure you use compressed air around the tank to ensure no debris falls into the tank, and if you must use a hammer and chisel to loosen it, make sure you are not hitting metal to metal. Bronze and copper head hammers work great too.