The judge signs off on the visitation arrangement that usually includes every other weekend and one weeknight each week for the noncustodial parent. On occasion, less time is agreed upon so go with what you have.
That parent should take a minute and look at his schedule and make proper arrangements to see his children. Usually a 24 hour notification is helpful so that there is no confusion plus it is just good manners.
If the noncustodial parent does not make any arrangements, there is no visitation. Plain and simple!
If this noncustodial parent is a narcissist, he will yell it from the rooftops that his child's mother did not let him see his own kids even though the reality of it is that he did not bother to make any plans or even bother to tell anyone he was, in fact, not even going to show up. Watch out social media, here comes a pity party. He will convince everyone around him that the children were not "allowed" to go. He is going to get his fill of sympathy regarding this so that in his mind, he did nothing wrong but that is okay, he is not really fooling anyone, maybe just the naive people.
Some people just really should not be a parent.