Opening the door can add to cook times. Opening at 3.5 hours then again at 5 probably added to the cook time. I usually dont open my door until Im at the 5 hour mark. At that point a hit with sauce, spritz of juice or whatever and let them finish. I try to only open the door that one time and will determine how much longer they need to go to get where I want them. I usually let mine get to the fall off the bone point, so 5 hours may be a bit long for babybacks for some folks that like a little tug left in them. I also cook at 225, but again its a matter of preference.
This is how I do it, but Im no expert. Just read read and read some more on these forums and also practice. Notes help a lot as well.