http://pokecharms.com/threads/official-pokemon-timeline-confirmed.10106/
I guess B2W2 and XY did happen at the same time. I could've sworn I read XY was afterwards and the developers were cryptic with the amount of time between them.
What I read was that XY take place after B2W2, and that they didn't specify the exact amount of time between them because they wanted us to guess ourselves.
^that one can't be true because according to the official timeline
Kanto & Hoenn take place at the same time
years later
Johto & Sinnoh (again same time)
later
BW, then B2W2 2 years after that
later
Kalos
TFW you get a drink to use for cooling off after exercising, but you forget you got the drink for that and end up just drinking it all right out of the refrigerator.