Make sure he gets a good night sleep,if possible(as I read in "Doonsbury" "there are very few problems on child rearing that can't be solved with duct tape.")
At that age it really doesn't matter. I was in the pool 24/7 at that age either practicing or just playing with friends. Don't let him get too crazy and make sure he gets a good night sleep.
Do you suggest a light or easy practice the day before swim meet? Or just let him rest for a full day? I am asking for my 7 yr old son.
At that age, they don't need a lot of time for recovery; as I'm sure you're well aware! Have him eat well the night and morning before the meet (not a lot of sugars).