How long does it take for the inside of the meat to get to 122F and since you don't get to boiling temps, how long does take to come down to temps after cooking? That is the worry window of botulism. Luckily it is pretty rare these days, but it can happen.
Good questions, I'm not 100% sure. On the cooling-down side, the general wisdom on sous vide is to eat it immediately, or plunge it into an ice bath to cool it down quickly right after taking it out of the hot water if you're not eating it right away. I wouldn't expect botulism to be much of a worry on the cooling-down side once it's out of the bag since botulism is anaerobic. In a an air-evacuated bag, the heating-up side of things has some potential for issues I suppose.
Based on the lack of a botulism epidemic amongst sous vide enthusiasts, my guess is if you keep things at a safe temp before the bath and do a rapid ice-bath cooldown on anything you're not eating immediately, the risk is fairly low, at least in the same
neighborhood of risk as any cooking that doesn't involve turning meat into a carbon brick.
