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Walls can be poured in temps down to about 20°F without too much trouble. The crete should be air-entrained. He may also call for some amt of calcium added to the mix which creates more heat when in contact with the moisture. They are also likely to mix with hot water.
Concrete makes heat as a byproduct of the chemical reaction. That and covering it with a wrap overnite help protect it. The idea is to keep frost crystals from forming before the setting action gets going fairly well.
The curing process continues indefinitely. In summer, nearly max strength is acheived in thirty days, with close to 90% in only three days to a week. It is a little slower in winter.
There are other more expensive additives to allow for colder winter pours but these are not likely practical for a normal sized home.
You mentioned an archy. He should be able to help you understand all this and communicate with the contractor on specs. That is what archies are for.