Quoting Linda:

Can I repot tomatoes a third time? They've already gone from the flat, to
an 8 oz. container, now in a 16 oz. container. They're already about a foot
tall

Sure you can. Be sure to plant deep into the new pot as more roots will
form along any part of the stem that is buried.

but can't go outside to harden off for about 3 weeks. I don't want to
kill them. Thanks!

Unless you live somewhere that the daytime temps are still regularly in
the 30's - very low 40's, I'd recommend that you get those plants
outside and put them in your garage/shed at night if necessary. It'll
be much better than attempting to carry them under lights. Caveat:
once you start the hardening off process, it's best not to put the
plants back under lights.

After germination, I keep tomato seedlings under lights for the first
couple or three weeks max, then out they go (after a hardening off
period). In general, if it's forecasted to drop below 41 - 42 degrees
or so, I put them in the garage for the night.

What zone are you in?