Hello, should I be concerned? They poured my basement this morning at 42 degree faranheit. It climbed to 50 faranheit this afternoon but it's going to be only 30 during the night... My foundation contractor tells me that it's not a problem since concrete curing emits heat and there is 1 1/4" plywood forms insulating the basement. I'm also thinking that there should be a good temperature difference between the air and the concrete due to it's thermal mass... Should I be concerned? I read that concrete only freezes at 28 faranheit...

I would not be concerned. It can be a problem if you are pouring midwinter when temps stay below freezing.

I would not be that concerned either, but if it may get any colder than that for the next few days (say the next 6, as it can take up to a week to cure) then you should try to protect it. If there is a problem, surface scaling is the first symptom you will see.