If you have it at all then you had it from the first day you played.
It doesn't actually end exactly when you get to Level 50, it ends at the next daily statistics reset at midnight PDT now or (PST in the winter). This is not something that many people know, and is not how that is worded in your Inventory, but is something my second account just noticed a few days ago.
Only people who started the game AFTER February of last year have that. Us players from day one thru people playing for about 6 months got ripped off when the Developers invented that.