Supposedly the 11th. If you check your steam badges you'll see the new mysterious badge waiting to get activated, its been there for a few days.

I've set aside enough cards to craft 44 badge levels, and have ~$15 in my wallet. If GTAV drops on sale I may have to pick up a steam card from Target. GOG and Amazon both jumped Valve this year, so hopefully they have some sweet deals to make up for the delay.