We haven't had that hard of a freeze in several weeks now, but I'd bring the feeders in overnight when the forecast warranted, replace them about a half hour before daylight because it seemed to me they needed the calories after a cold night without waiting for a thaw if freezing occurred. Nothing scientific there, just my feeling :) I will find them at the feeders before its really light out, and tonight - a rufous still at the feeder as it was getting too dark to see him.

The annas winter here, manage a few nights in the teens and appear no worse for the wear if food is available. Frost shouldn't be a problem.

I'm also in eastern PA still waiting on my first sighting. I'm near Reading.