I like Manpot's suggestion too but it will be a lot easier to stop and check if you hire a private taxi. We had a van full of groaners and a driver that insisted the only ferry was in RH and didn't want to stop. Then what do you do? I'd talk to the driver before you leave and tell him that's what you want to do, it could avoid a bad scene in the cab.

Like sail2wind said trying to get to RH before 5pm with a 15:53 arrival can be difficult. Several things can conspire against you. Late flight, baggage takes 15 minutes to show up, you are first on the van and it takes 10-15 minutes to load it full, traffic that time of day and a few people that need to be dropped off along the way. It can work out but it will probably be very stressful.