Each steam-trading-cards-enabled game has a certain number of cards that are automatically earned just by spending time playing the game. (3-5 from what I’ve seen so far) What I haven’t been able to figure out is, how long does this take?
How many minutes do I have to spend playing each game before I earn the first (and second, third, etc) card drop? Is it randomized or fixed? Are they the same for every game?
Typically you get one drop about every 15, 30 or 60 minutes of “gameplay” depending on the game.
By gameplay, of course, I mean “have the game running”, and by “have the game running” I mean “the border of your avatar changes from blue to green.” For example, for Trine 2, idling in the launcher counts as gameplay.
Hot Trine 2 gameplay action
From personal experience, it appears that you can get a drop every ~15 minutes so long as you restart the game after every drop.