Time limit for a 200 is 13:30 or 14 hours. Starting at 8 means finish closes at 21:30 or 22:00 which will be dark for most of the year. BUT most people don't need the full time limit on a 200.
There is always a compromise between starting at a civilised time and avoiding riding after dark at the finish.
I find I don't sleep well when I set my alarm earlier than 7. So an earlier start would deter me. As someone who typically gets round a 200 in 9 to 9.5 hours is be gait with a later start, but in aware others would not want to finish in the dark or even after the pubs close.
I've ridden a 400 that started at 12:00 which allowed for a sleep stop at 300km saving me booking two nights accommodation which would have been required with an early start. And also a 400 which started at noon and I reached the finish at 7am suitable for getting the first train home. So 12:00 for 400s seems good to me. There will always be one night of sleep list, better not to compound that with a 4am alarm before the ride starts.
But I also like the idea of starting in the evening and riding through the night while fresh, as per the start of PBP or overnight 300s certainly feels better than reaching arrivee at 2am too late to check in to a room and too tired to drive home.