My DS10 had a spinal fusion (C1-C7) done 2 years ago this past March.
He was in vest and halo device for about 6 months after the surgery.
He was up and cruising the hallways of the rehab floor, the very next day.
We were told he would need extensive therapy for about 4-6 weeks, but he did so well, therapy wasn't needed for longer than a few days and we were discharged in about a week. Everyone heals differently, I think the recovery time for my son was so quick because he has been through so much in his 10 years, at least 5 surgeries, that he has just become accustomed to the discomfort, that nothing slows him down!
We went to WDW 1 year after his fusion and followed the doctors instructions - NO roller coasters, NO Tower of Terror, NO Dinosaur and in general - nothing that was going to bouncy him all over the place. It was my understanding that these would be our guidelines forever. Not that he was a big fan of any of these things before the surgery.