Wow, Jason.
Just think if you had a few inches of snow on the ground. Your temp probably would've dipped to zero. Snow, can fall, here, into April. Detroit's average for April is one inch. Such late snow usually doesn't last, though, because of an increase in sun angle, and increased daylength. Today, at 42 degrees N latitude (Detroit), dusk arrives around 7:40 p.m., and daylength will continue getting longer, until the first day of summer. Around that time, dusk will arrive around 9:30 p.m. Believe it or not, daylength in summer, lessens, the closer you are to the equator, but increases the closer you are to the North Pole, where daylength is a full 24 hrs, on the first day of summer. All has to do with the tilt of Earth, and which hemisphere is receiving the most direct rays from the sun, on the first days of summer and winter.
Your palms may do alright. I think others on this board's palms have seen such temps, unprotected, and lived. Some have reported frond loss, or having to trunk cut.
I know it could be disappointing though if any damage shows after the palms had been protected, all winter, with no damage, when the protection was removed.
I knew that March (April, too) has roller coaster temps, with wide swings. My palms are still covered, for a little longer.