If you're dead set on foiling, like others have suggested, I think one hour is tops for baby backs.
I saw a video recently of a guy smoking racks of spares at 250. He foils when they "look the color you want 'em to look when done". He starts checking the spare ribs after they're wrapped for just one hour, looking for pull back from the bones. (On this video, he unwrapped after being in foil for just an hour and a half.) Anyway, he cooked unwrapped for another hour with sauce for the last 15 min. 
All this to say that I think I haven't been happy when I foiled ribs because I was thinking "321 method", instead of knowing what to look for. With baby backs, I'd check 'em probably no more than about 45 min. in foil.
Good luck and let us know how they turned out!