I wouldn't worry too much about stats. Go for what suits you best.
It's certainly true that an 18-1900 start with bad weather gives a very unpleasant leg 2 in the dark. I recall one night it being impossible to even follow the path from Clough Head such was the wind and rain. No fun and very hard to stay on pace.
That said, were I to go round again I'd still go for that start time as, like Stolly says, 00-0100 is just too late for me to feel good at the start and in good weather leg 2's a doddle, there's nothing to slow you down.
Of course a normal morning start time going a/cw is an option, but that's a whole other discussion...