As long as its above freezing outside they can definitely stay outside. If you are at risk for getting a frost again then you have to decide if you mind possibly having to bring them back inside again or not. I have left my Queen palms out with temperatures in the 30s with no problems. Slight frond damage begins when temperatures are in the upper 20s (potted plants are a bit more suceptible to cold than plants in the ground).
Also make sure not to bring them out into the full sun right away! That will burn the fronds.
Good luck!
-Alex

Not sure what part of Michigan you're in, I'm in zone 6b so probably warmer part than you, but I've had all of my palms out for the last couple months, and the last time I brought anything into the garage was a couple weeks ago when temps dipped into the 30s at night. As long as you're not in Northern MI, I'd say you're safe.