Easy for someone as quick as you - either go with the first group to leave (usually a mixture of slow and fast riders) and wait til the fast guys come past and jump on to them. Or wait around a bit as there's usually a few fast guuys who leave it about 15 minutes then try and catch everyone.
The way I see it you may as well start riding as early as possible to keep warm.
You can never be sure who's going to be out. Depends on the weather. Last year saw a handful of elites 1sts and 2nds as well as dozens of 'ordinary' riders. I stayed with it 'til Groombridge then got slaughterd by Chas Hollosi and Reg Smith
Course you could just sit in a nice steady group which is probably what you should be doing at this time of year
Usually leave promptly at 9.00