I talked with a local stray rescue group who supports TNR, and they also thought the 10-12 days was overcautious. They said you need to balance the extra recovery time with how stressful the confinement is for the cat, because if they end up thrashing a lot or chewing on the wound, it's riskier than if you let them out.
Robert isn't as bad as a full-bore feral, but he's definitely stressed. He's constantly rearranging everything in the crate; since the surgery he has started turning his litter box upside down and chewing on the edge. He's left the surgery site alone so far, but he has been biting on some of his other fur.
After extensive searching for other vets' online post-neuter-recovery instructions, the longest recommendation I could find was to keep them in for 48 hours. That was a regular vet site, not even a TNR one. So I remain confused by the huge variation in opinions.
I need to go with my gut. It would be ideal if I could keep him for the whole time my vet recommended, but given the balance of all the factors and the conflicting advice, if he's OK after 48 hours then I will let him out.
Poor Robert, I set out trying to do the right thing for him, and now I feel like I've just been cruel.
We have at least two more cats to TNR, at least one of which is female. We are definitely going to have to come up with something better than that one crate.