I don't ever remember seeing a Tweet re: different set times for both weekends before, which might be a subtle indication that there will be some noticeable changes for set times between both weekends.
There was the Avicii modification in 2012 and the Blur/ Stone Roses switcheroo last year, but otherwise everything generally stays the same.
Also of note is that the Pixies and Julian Casablancas are not on the poster on the website yet. Could these be W1 one-off gigs? Other set of surprise acts W2? Nothing for W2?
This could all be originating from a sense of unsubstantiated paranoia that the Pixies/ Casablancas might not play W2, and that other acts will go from day to night and vice-versa.