Keri, congrats!! You'll be so glad you did it.
Kody was supposed to be on stall rest for two weeks (my choice- the vet who did it said to turn him out like normal the next day, my own vet said to keep him stalled for 90 days
) but I made the mistake of letting him out the next day "for just a moment" while I fiddled with a gate and the result is that Big Blue Ball video on YouTube. Little brat was galloping around and mauling a ball!
I did keep him in the stall with daily handwalking the first week and a half but after that I gave in and let him out as unlike the splitting surgery Kody was clearly healing quickly and not in a lot of pain. I kept a little diary of his recovery and it notes that by week 3 he was standing squarely on both hind legs again (he'd been doing this weird contracted stance on his toes after the surgery which I think was related to his atrophied muscles) and by week 5 he was driving straight lines and could treadmill without soreness but couldn't track up on any kind of circle. I turned him out with a colt in week 6 and the manic racing in large circles was clearly too much for him, he was sore in minutes. By week 7 he was no longer using both legs together to bunny-hop into a canter and was trotting out freely. By week 8 Kody was back to real work doing lessons and a short schooling trip to Happ's although I still felt that he could easily overstrain himself and he did tire out after 40 minutes or so when he'd usually go for at least an hour in that condition. In week 13 he went back to doing jumper and liberty and by week 14 he finished and won a major CDE but that was a real stretch for him. By week 16 however he was stongly back in the game and finished another CDE in fine style, not even tired.
Kody's example is probably a worst-case scenario as despite years of correct driving he was severely undermuscled in the hindquarters from this condition and had to rebuild his movement from scratch. He was bilaterally affected and locked with each and every attempt to walk unless he was in harness so I suspect part of his recovery time was the soreness of using new muscles and learning to move in completely new ways; I doubt for instance that any other horse would have shown the tippy-toes thing he did the first few weeks. On the other hand while Kody turns out to have had a lot of weakness back there he WAS fully conditioned for long-distance driving and it still took him that long to heal up so I don't think horses recover from this quite as soon as some people would have you think (i.e. back to full driving in a week like nothing happened). Heck, what's the rush? You're doing this so the horse will be sound in the long term and it seems to me that it's foolish to jeopardize that in the first few weeks. We're told not to longe horses with locking stifles because circling puts too much strain on the inside leg and I think that's still true as the horse heals. With large horses there is a slight danger that you could fracture the patella through too much strain until the scar tissue has built up and stabilizes it and that's why my surgeon recommended keeping the horse confined for so long.
Just take it easy and look to your horse for clues on what he's ready for. I think for arena driving he'll likely to be fit to return to regular work by week 5 or 6 and could probably be ground-driven several weeks sooner but that's only a guess based on my own experience and allowing that your horse probably has fewer issues than mine did. Many people resume normal activity much sooner and if your horse seems fine then there's probably nothing wrong with that. The important thing is to take your cue from him and not from some external timetable. If he's not healed, he's not! This is a great time to go for long straight walks/ground-drives/drives in the country and make a return to tight turns and figures the last thing you resume.
I hope this works out for you as well as it did for us! I've only had the one horse done and am a well-known conservative so take my advice for what it's worth. The worst that is likely to happen is that your horse heals much faster than I'm indicating!
Leia