Real smokers burning wood/charcoal are a much drier heat. They also have to deal with the temp possibly running high. And, pork butts take 3-4 times longer than baby backs although seems it would be hard to hold temp opening any smoker every 15-20 mins but whatdoiknow about your neighbor.
Your grill won't smoke to the same level as a purpose built smoker so you can probably smoke them the whole time and depending on temp (250-275) you'll be looking at 4-5 hours. You want to see the tips of the rib bones to start getting exposed from the meat pulling back (at least 1/2"). If they haven't caramelized you can turn the grill up for a really quick browning but be careful if you've sauced them. Burning propane creates some water vapor that helps keep things a little more moist than but it can also prevent the ribs from getting a crisp outer layer like a real smoker would create.
Slather the ribs with yellow mustard before the dry rub. 2 gallon ziplock bags are very handy for this. Also, peel the membrane off the back side if it's still there.
* i've used my propane grill for smoking ribs