I'm not a fan of the DLC, cosmetic or not. They're pretty damn expensive for just being cosmetic. As many have pointed out some of them cost more than games sold on Steam. From my understanding you're meant to be able to unlock them in playing Portal 2, but as it stands I've beaten the game n played half the co-op and all I got was a companion cube hat. Which Duke had too so I assume that's the "you beat Portal 2" unlock. It's the kind of stuff that before DLC would have just been unlock content. Play the game, unlock stuff, personalize your co-op bot. Beat the game, get a hat. Open your wallet, get every colour in the rainbow.
My only thought is they're running them like TF2 drops (which doesn't make sense since it's a primarily linear game and SP on top of that) and it all drops, but only 4 times a week or whatever every 8 hours.
As for the time I theoretically took 12hrs or so, getting it at about 11am in morning n playing till about 11 at night. But counter in watching house, lunch n tea, etc it knocks off about 4-5 hours.
btw anyone get a Citadel vibe in parts of the game?