may I plant custard candy daylilies the day before an early freeze

I would not plant my daylilies 'the day before' an early freeze. I try to get mine planted a few weeks before the first frost. I'm in zone 8b...Georgia. We get a few nights below freezing, usually in January or February. A few of the other very knowledgeable members in your area may chime in as well.

Where are the daylilies now and where did they come from? If they’re already acclimated to being outdoors in your climate or a colder one, then it shouldn’t bother them any more than it would if they were already planted. In fact their roots will be more protected in the ground. If they came from a warmer climate and are indoors waiting to be planted then I would wait until the freeze is over. But it would have to be a heavy freeze to be a problem anyway, since the soil stays warmer than the air temperature and the perennial parts of a daylily are in the soil. So the answer would be it depends on the circumstances.

Daylilynut I agree with Sooby. Here in Z:5 I still have plants to put in the ground. They have been outside. Below freezing temps are expected overnight. Going to do my best today to get them in the ground and mulched. I said that to say it will be easier to put them outside than to try and keep them
alive in the house all winter unless you have time and means to do so. Just pile on the mulch
I have planted daylilies around here in November in years past that survived. I believe that they will be fine if they are not sitting in a soggy area.

Custard Candy is a fully deciduous, (a.k.a. dormant) and hardy (cold-resistant) daylily that has been successfully grown in Ontario, Canada, (Zone 3). Mine are already underground for the winter.

I'd go ahead and plant it. Water it in afterward and make sure that the crown (where the leaves meet the roots) is about an inch under the soil after watering/settling. Since it's a newly planted daylily, I think the biggest problem you might have is that it won't be anchored well enough to resist being heaved out of the ground by frosts. If you're worried about it, throw 6-8" of leaves over it along with some wire or plastic mesh to hold the leaves in place.