Klepper says the Aerius Expedition II+ 545 has a volume of 600 liters. Having owned a AEII and now a MkII, I'd say that's a reasonable estimate for both boats. So call it 160 gallons. Or 20 minutes of pumping. I think realistically, you'll pump for 30 minutes.
I'm planning a Montauk to Block Island paddle early summer, and we're certainly using float bags and the spray deck. Bailing out a MkII would be a fun stunt in a warm lake on a summer day. Not so awesome in rough water in Block Island Sound.