Summer is good – the days are longer and the water warmer etc. Around the longest day has its obvious attractions but beware of the weekend nearest the longest day and the one before that, there will be a lot of traffic related to National Three Peakers using Borrowdale 24/7. Time of day?
Clearly entirely your decision and some of the factors to consider are discussed under the advice on each leg.
However some major factors are:
1) Dangerous to cycle this route in the dark as fast descents and sometimes very poor road conditions. 2) Swim conditions re waves and traffic better early morning. 3) Scafells unpleasant in the dark. 4) Starting late in the day means longer overall without sleep.
I would suggest overall 6.30 am may be the best if using a 24 hour schedule and the same run direction as I did. It would allow you to get down Wythburn before it got dark.
Although not particularly relevant here for those desperate to know McAvoy’s rule number one states that “95% of men have balls bigger than their brains and the other 5% have something seriously wrong with them”.