First of all, I am probably the last one to offer and opinion, because the idea of more than 6hours in the saddle in any one day is not at all appealing to me.

But I would echo TriGirl's concerns... if its 9+hours in the saddle with minimal time for breaks, in winter when dusk and dawn do NOT stretch out helpfully like they do in summer... well, I think that is not enough time.

With this many bikes involved, and so many miles, its not a matter of hoping not to get mechanicals (like flatties) its a matter of how many... that will stretch your day out. And if you are anything like us, flats (for example) tend to happen in clumps and we might change four in one day and then nothing for days and days...

I guess if you all had lights on your bikes and wore good reflective gear, and maybe started before (or, at the latest, as) the sun rose... that would make me feel more comfortable if I was waving you off the start line.

All the best. You are a bunch of experienced cyclists and I know you'll consider this from many angles and make it a safe and fun day.