I've not even thought about finishing time. Anything could happen. I'll be plodding (relatively speaking) because I'll have done a 600 the week before and the massive Pendle 600 is the week after. So, if there's trains available I'll take one, if not I'll ride home.
SE London.
I suppose the 7.30am start would allow a train arrival, but would mean finishing later which could be an issue with getting back.