I'd personally try to keep them inside. It probably won't hurt them in the 30s but I wouldn't risk it. You made it this far with them, what's another month of work...
i should have risked mine outside. i have 22 acorns that had sprouted and were between 2-3 inches tall. a few had tiny leaves starting to unfold. my hound, last night out of boredom, chewed the leaves off of 4 of them and pulled out one rootstock from a pot.