When both parents have signed an "Agreed Temporary Parenting Plan," will this document become null and void if one parent does not follow the terms?

Both parents and child reside in Florida. In the "Time-Sharing Schedule," it states that when the parent has the child for an overnight that the parent's time begins after school. But, one parent refuses to pick up the child after school (2 pm) dismissal stating that he/she works until 5 pm and could not get child in school's after care program. The other parent also works until 5 or 6 pm, and has to make arrangements on the other parents days to pick up child from school when school notifies that child has not been picked up. On those days the child has been waiting in the school's office up to 4 pm. One parent has made appropriate arrangements to have a family member pick up the child after school on their days and now has to scramble for care on other parents days because that other parent just leaves the child at school after hours with no care. The other parent then picks up the child after his working hours for the overnight when it's convenient for them.