Cooked a lot of Ribs at 225, cooked a lot of Ribs at 275. I've never had a rack that only took 4 hrs to complete. But I cook my ribs naked (no sauce, never foiled) with just rub. Doneness test I use is standard bend test (grab the end of the rack w/ tongs, the opposite end should be drooping toward 70-90 degrees and the meat should just be starting to pull away from the bones). When you cook half-a-rack, then test with the toothpick between bones for meat firmness.
Not all ribs are created equally, some Baby Backs take as long as the St Louie cut, some an hour less. Mine usually take 4.5 to 5.5 hrs for BB, and an hour more for St Lou. at 225. I use Maverick 733 to measure cooking grate temp, not the lid dome thermo.
Ribs, they're what's for dinner ... ummmm. SJ