22nd April ;)
EDIT: for EU and Australia it's 27! :D :D :D Yay!
Actually... it is April 10th in north America and April 22nd in Europe.
Note that the event to get the Liberty Pass ends on those dates, but once you have the pass you can get Victini whenever you want - today, tomorrow or in 6 months time!
Wrong, I read it was April 10th.