cut down to 3-1-1 I've never been able to go more than one hour in the foil without turning them into mush.
St Louis ribs are not equal and come in different sizes. Some can be meaty while some thin. so the cook time will vary.
Use the bendy test (do they bend 90 degrees when picked up? and the toothpick test (slides easily) and use your eyes (meat pulls back about 1/4" - 1/2").
When you take them out of the foil, you will have a good idea how close to done they are.
Sometimes, they are ready and just hit them with a quick glaze for 15 minutes and get them off to rest.
Other times, they aren't close, so take them out of the foil, close the lid and check back in a half hour. Once they start getting close, sauce them.
2 WSM 22
La Caja China #2
Weber 22 Kettle
Brinkman Vertical Charcoal (out on loan)
Weber Q 200
Weber Summit Series Gasser
super sneaky thermapen disguised as a protemp