Generally in a contempt hearing the court will set an amount he has to pay by a certain day. If he does not, the standard jail term for a first time offender (usually after many warnings from the judge or magistrate) is 30 days. He can get out of jail by paying what the court order specifies.
Your husband can also usually avoid jail time by making his regular payments every time he gets a paycheck (in fact they should be taking it out of his paycheck).
He doesn't get any credits to his support amount by sitting in jail. That's his punishment for not paying.