Andy, as I recall, the 0800 start time is for those who think they'll be very slow - there was a cut-off indicated somewhere of seven hours - everyone needs to finish by 1600 hours (4 pm).
ALL: near the end, when you've turned from Addiscombe Road into Sandilands, FitzJames is a LEFT not a right turn to reach & cross Mapledene and reach Uplands! (and near the start when you've gone along the edge of Lloyd Road and across Coombe Road, it's right-then-immediately-left into Campden Road). But I'm sure it will be well marked tomorrow.
Also, there's a sign on Addiscombe Road saying that Addiscombe Road is closed from Shirley Road to Sandilands tomorrow for a Triathlon, but Ian says it wasn't a problem last year and they let people drive in okay. (Alternative route would be along Lower Addiscombe Road, left into Clyde Road and to end, left into Addiscombe Road, Right into Radcliffe, left into Haveland then Right into Sandilands - but I'm hoping not too need that detour!)