If they are meaty loinbacks, you only need to shave off a little time. Better yet... Plan the same amount of time, and use some of the foil time holding in a cooler if you are way ahead of schedule. IMHO... There is a lot larger margin of error with babybacks.
If they are trimmed babybacks without any meat above the bones... First, I'm very sorry....But, cut your time almost in half.
I bet you will end up being pretty happy with everything. The loinbacks have more flavor than most people expect with plenty of meat and fat. I'm sure you will knock 'em out. Have fun.