It varies every year, so there's no point in guessing when it'll be. They may not even release the update until May. They have to test it and make sure things work and no problems occur. You'll know when there is an update as Steam will update(if you have auto updates) and SI will announce it on here.
Doesnt really matter what date it was last year, plus it was slightly late last year if i remember correctly, like i say there will not be anything until after the transfer window has closed, most likely mid to the end of feb.