I agree with determining the flow in gallons per minute from your source. I did it years ago for my home spigot, and it makes things much easier. For example, my flow rate out of my spigot (with the tap spun 180*) is 5 gallons per minute, I have 80 gallons of fresh tank capacity in my trailer, so it should take around 16 minutes to fill the on-board tanks. Add one minute if the pump is on and the hot water tank is empty as it will fill up as soon as the pump is turned on if there's water available.
No way it should take an hour to fill tanks unless you're dealing with VERY low flow.
Now draining them? Yeah, I would believe an hour. It takes more than that for me to drain full tanks on my trailer. Even if the drains are open, it would only take about 30 minutes to fill the tanks at the most. And I've done this. I put the hose end in the fresh water fill and walk away and come back about 10 minutes later and the drains have been open the entire time!
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!