Cold Temperatures

I've read the preparing for winter thread, but notice most people have coops. My girls free range. I have RIR's, whites, and EE's. In anticipation of this big cold front, we built a covered area and put their food and water in it to entice them in. They hate it. Now, the weather channel has us down to 29 for up to 8 hours tomorrow night (far North Houston) and they won't go in. They are all up on their perch on a fence. It is blocked on one side from a wall, one side somewhat by tarps, but the other two are open. Will they be okay? We don't usually get this cold in November, so I was really expecting a couple more months. Should I wait until they go to roost tomorrow and pluck them up and make them go indoors? I know it isn't that cold compared to what so many have to deal with, but they don't have any real cover and won't go in.