If cleaned before you shoot, then you should be able to shoot 300 shots without a hitch - singles, caps and doubles. Even if not, you won't need to clean until you get to doubles. I reload, so the shell catcher keeps me from having to bend over so much to pick up hulls.
If you do have to clean it, it will take about 5-10 minutes to get to the rod that extends from the magazine, clean the powder residue off, and reassemble. That will get you through bunches of rounds. Since you have an hour between singles and caps, usually, and then another hour before doubles, I don't see that time is the issue.
My Browning GTI and Browning BPS Trap guns kick pretty hard, as compared to the 391. When you clean your 391 (or 1100/1187) think of it as "caressing the parts of the gun that kisses your cheek" as opposed to not having to fiddle with a gun that punches you like a right cross.
Danny