Legal Question in Family Law in California

There is little to nothing the law can do to force a parent to be cooperative. What it can do is force a parent to comply with a court order. If your fiance and her ex do not have a co-parenting relationship that supports flexibility and cooperation, she is simply going to have to face the fact that his time with their son is his time and she has no legal right to make ad hoc changes with the child and expect the father to abide by them. There is no legal right to anything but adherence to the court ordered schedule.

On the other hand, if he is not abiding by the court ordered schedule, she does have the right to ask the court to find him in contempt, which can result in fines, community service, and even brief jail time if it is egregious enough or continues after lesser punishments have been tried. The court is not going to be interested in "he always drops the kid off 45 minutes late." But if he refuses to return the child for days at a time. Or shows a consistent pattern of significant deviations from the ordered schedule, your fiance can file an OSC re: contempt which is a scheduled hearing at which the ex will have to appear before the court and "show cause" why he should not be held in contempt of court.

The other alternative, if a parent is not TAKING their custodial time, i.e., is constantly not showing up for their time at all or always calling and cancelling their custodial time or visitation time, that is grounds for altering the schedule. Again, you file an OSC, but for modification of the custody order, rather than for contempt.