This would depend to a great extent on the rules that a given state or locality has. Different states and localities will have different procedures for what must be done in order for an ordinance to take effect.
For example, in my town, a proposed curfew would be treated like any other proposed ordinance. The proposed law would have to be read twice (usually in separate meetings of the city council). Depending on the kind of law, it might have to have a public hearing.
From there, all it needs is a majority vote of the city council. The mayor signs it, but that's a formality because there is no veto here. Once that is done, the law must be published in the local paper. Five days later it takes effect.