Those early starts are a bummer. Doesn't matter what time it is though- you still have to be there. Done 6am rides in which the Tandem has to be assembled before hand so that would mean leaving the hotel by 4.30 and getting to the venue by 5.

But the London to Brighton has staggered starts which are "Pre-Booked" Earliest start is 6 am and that is the best time for any grade of rider. From 7am onwards you will be slowed down with the sheer numbers on the hills and an 8am start means you will be walking those hills due to no room left from the walkers. 9 am start and you will even be walking the slopes.

Good job on the ride. Although fitness will help in the last 20 miles- better pacing and energy food at around 70 miles would probably work better

Till you get the fitness to gain a "Platinum" status so you can get lazy with an extra couple of hours in bed. I love being lazy but I am afraid you will have to work for an easier time