In my view the 18h start time does make it harder, by a margin. The trouble is that there are no 24h facilities at all, which includes street lighting! So, we set off with the first control at 45k - the organiser stamping our brevet cards in a field just before Ypres and then it was a dark, unlit, no break/control, in-the-middle-of-no-where slog until 186k. I arrived at 01.45. Again, the organiser was stamping cards in an unlit car park before another 100k. By 8am and 286k, I would have paid several hundred Euros for a coffee or something, somewhere vaguely warm and/or a little rest. On longer rides, hot food and drink is the key for me.
That said, I did know this before I started and I was using it as good PBP practice
The route was wonderful.... and shocking at times to see fields of graves, not to mention the number we passed.
Compare this to the 400k "norm"....a 4am start on a Saturday so after 2hrs, the sun is up, by 7 the bakeries are opening, and after another hour, the cafes are opening. The controls are every 60k or so, each one in an open cafe. Finish by midnight, so only half the total night time cycling compared to this ride.
I'll take the latter, any day - but it's horses for courses. Each to their own.
I took 2x800ml bottles which were re-filled at 186k. Not much, but it was night time and fairly cold so I didn't drink as much as I would on a daytime ride.....when the cafes would be open.