With Baby backs think more around a 2:1:1 than the 3:2:1 for spares.
2 hours bone down meat up in the smoke.
1 hour bone up, meat down with some apple juice in the foil, (or less I often only use 45 minutes in the foil on baby backs).
1 hour back out of the foil, bone down, add finishing glaze 2 or 3 times building up the layers at 30 minutes, 45 minutes and 55 minutes into this hour.
The other things that will help are to buy yourself an oven shelf thermometer, they cost about $4.00 at WalMart, not very stylish or sexy but they do the job.
Then the next time you are setting up to cook, "map" the temperatures across the whole of your cooking surfaces, before the start put the thermometer on one of your grates, at one end and either in the front, the middle or the back, close the lid and fire up the pit, wait till the temps have had a chance to stabilize.
Pop open the lid, note the reading on the therm, move the therm to the next position at that end of the grate, close the lid allow to return to stabilized temperature, pop the lid take another reading, move the therm.
The simplest map on a “normal” sized grate will have 9 readings left (front, middle and back), center (front, middle and back), and right (front, middle and back). There may be variation between left and center and right and also between the front and back in all three, but this will give you a more accurate view of the way your pit behaves, and just how true the thermometer on it is!
If you have a longer than normal pit, you might want to take more readings to more fully cover the whole length of the pit, once you have the map, you have clues you can use to either tune the heat in the pit to reduce the differences or to learn to cook on the pit as it is and to use the heat differences as part of your cooking process, allowing you to move things that are cooking faster than you want to a cooler part of the grate, and move things that aren't cooking as fast as you want to a higher heat, to increase their cooking speed.
But the place to start with either is the temperature map of the whole pit.