Hi Steampig,
Now the date has changed to April there will be less daylight so I assume the grouping times may be brought forward, making it even more difficult to get through Fleet Moss before grouping to minimum group size. It depends on your speed, but speaking for myself it may relieve the pressure for speed during the daylight hours and I can just resign myself to grouping at Fleet Moss.
I think the advice offered by others cannot be bettered - i.e. don't set off too fast. Run or walk at a pace that feels comfortable and sustainable, eat and drink well, let the necessary time elapse (about 1.5 times what you'd expect for a 'trail' event) and you'll finish feeling fit and well, if a little used. The overriding longterm emotion will be one of proud achievement and camaraderie.