Sorry to say it, but that all depends. It depends on the meatiness of your ribs, the humidity, the phase of the moon, they way you want your meat to be when it's finished etc.... For me, given the way I like ribs, I'd start with an hour and a half in the smoke, an hour in foil and then maybe 30-40 minutes back on the grate without foil. Just keep an eye on them. There are so many variables it's impossible to give an exact time. Since this is your first attempt, I'd suggest sticking to 225˚ and the 2-2-1 method. The reason being, it's been thoroughly researched and it works. Plus, at the lower temp, it'll give you more leeway. I'm not saying this stuff is difficult, but it does take a good bit of trial and error. I'm hoping you're not doing these ribs Saturday for a huge family gathering or something. If so, I'd get to the store now, stock up on ribs and start doing trial runs!! Also, read through the posts here on baby backs. There's a lot of fantastic information here, much better than any advice you'll get from me. Good luck and let us know how it goes.