Generally it's a 1/2" joint. For a project like this, we will use a 1/2" tear away foam expansion material 4" tall. It comes in rolls usually 50'.

The top 1/2" is perforated so it can be torn away. The space is then filled with a self leveling, flexible material to allow for expansion and contraction. Deck-O-Seal is the most common brand used.

There's no problem pouring concrete in cold weather provided additives are in the mix to prevent freezing and allow for a quicker set. This is customary for any qualified mason to know.

Thank you for your insight. I expected a 1/2” joint.