I’m not surprised you didn’t find it, because the full itinerary hasn't been announced yet! Won’t have this info until approximately April/May (depends when the snow melts in the Alps) when the second reconnoitre is carried out.
Mileages vary from day to day depending on what route, tasks or activities are happening on that particular day, but to give you some sort of idea it can be anything from 253 – 487 miles, the longest day being 08.00 – 18.00 hrs.
Of course days could be a lot shorter, but that would involve hundreds of miles of toll autoroutes, something that none of us want as we have enough rubbish driving in the UK as it is. If the driving experience isn’t pleasant, what’s the point? Trust you agree.