My ex pays me a laughable amount of child support (for the state of California) which is my fault to agreeing to it to get things rolling on the divorce... ANYWAY, he says that when he has the kids that month he either is not required to pay the support or if the days he has them does not total a month the support will be retro-ed. He asso has been post dating half of the child support until the 15th. Is this legal.