Do substances have to be cold to freeze?

No because anything can freeze but the warmer it is the longer it will take to be fully frozen. If you want the substance to freeze faster have it be cold by putting it in the fridge or something.

No.

Explanation:

90% of the time when someone hears the word "freeze", they think cold.

However, at its core, to freeze, is to become solid, and there are many solid materials that aren't necessarily cold, for instance Lava is hot, and once it cools it becomes a form of rock that is not necessarily cold, however it has frozen into a solidified form.