I dont think me telling FI he CANT do something would go over real well, lol, and vice versa. But I would certainly express my concerns and voice my opinion. I can see why you would worry if he's there on time, etc., etc., but I think if you just make it clear what time he needs to be ready to go that should be good enough. Like the other gals have said, it is his wedding day too and might do him some good to unwind and enjoy being out with his buddies before the big event