Firstly, I am glad to see there's others who think that it's a bad thing to rehash Kahn for the sequel to Star Trek. I'm against it, mainly because the vibe I am getting is that "This is a new timeline, now we can do Kahn MY way, hahaha!" Considering how new this timeline is, and the current setting (and when they net Kahn in TOS), I don't see how it can work out for the sake of argument that it can be done because its a new universe. Not to mention the appeal on Kahn, was that he was a challange, an opposite, to an experienced
James Kirk, not someone a couple years into his carreer period, let alone command.
Secondly, I am confused they would have to change the days 'because those dates already happened' as it's fantasy/science fiction/fake/whatever term you want to use, anyone who wonders where the Vulcans are come 2063 IMO, is someone who'd need serious mental help.