I need advice for keeping the last baby alive. He is probably about a month
old, I can't be sure because I just haven't had any wild rabbit experience
before. He is getting warmed evaporated goat's milk fortified with a bit of
cold-pressed rice bran oil, rice honey, maca powder and strained rice
porridge, as much as he will take, every 2-3 hours.

Assuming he lives, how long should I keep this up before turning him loose
(far from the house - and cats - of course)? Also, is there a better formula
for rabbit babies?

Baby rabbits are tough to keep alive. Generally mom puts her babies in a
shallow nest lined with dry grass. She leaves all day long to feed them comes
back at dusk to feed the babies. If the baby is injured, mom won't take them
back. If you were to have put the baby back in the nest, locked the cat up, and
mom didnt' get the baby and move it by nightfall, mom is dead. Contact a
rehabilitator to take care of the baby for you. They have all medications,
special feeding supplies and special formula besides years of experience.
Here's a list, find one in your area
http://www.tc.umn.edu/~devo0028/contact.htm Sooo much easier and the babies
have a better chance of survival.