A lot would probably depend on the alignment of the ribs post fracture, and the stresses encountered during healing. I have cracked ribs a number of times and a couple of months seems to be about average for me.
Six weeks. That’s what I was told, that’s how long mine took, with gradual improvement from week to week (as in being able to sleep in a prone position vs in a chair).
I do heavy physical labor from sun up to sun down. This was almost impossible the first 2 weeks, but 3-5 weeks only painful upon squatting or twisting. After six weeks, only an occasional twinge. Now it’s good as new (about 10 weeks).