You'd have about 20 minutes, which is how long it will take for the Maryland State Troopers to arrive, once they get the call.
And I'm just kidding... You don't have any time at all, because you can never tell if there might be a Trooper in the restaurant.
The Riverboat is IN Maryland. All the normal, insane, Maryland gun-laws apply once you cross the mean low-tide water line.
Don't do it. At all.
My humble advice.