People and injuries vary so it's impossible for us to say. I recommend following Wogster's advice. As a comparison point, I broke my hand two years ago (third metacarpal) when I was 48. I was back on the trainer about two weeks later and rode a 6-hour with the cast still on (the race director let me drop down from the 12-hour) just 4 weeks after the injury. I did not require surgery. It was an option, but I opted to have the bone pressed back into place as the cast was hardening. I did have occasional throbbing pain for ~3 weeks after the injury and I think the light exercise on the trainer helped reduce it.