Divorced couples are known for not being the best of communicators, and even those who manage to have a fairly civil arrangement can find themselves dealing with little annoyances such as one parent being late for a dropoff. In most cases, these are infrequent and are best dealt with by just letting it go. However, in habitual cases, a stronger approach may be needed.
In most cases, habitual tardiness is just a personal habit issue. Some people are just constantly late. If this is the case in your situation, you likely already know that your ex has issues with punctuality. When the habitual lateness causes disruption in the children's lives, such as making them late for extracurricular activities or keeping them up past their usual bed times, it may be something to address.
The first step in dealing with these issues should be to attempt a civil conversation with your ex about the lateness issue. It's important that this conversation take place away from the children and preferably on neutral territory. Try to focus the conversation on how the actions are affecting the children and not judge your ex's tardiness.
If this approach doesn't work, it may be necessary to address the issue more formally. It is possible to petition the courts to enforce the current visitation schedule. If your ex continues to be late, it may be possible to file contempt charges. It's important to note, however, that for the courts to intervene, the lateness needs to be causing an issue with the children and not just be an irritation to you.
Source: FindLaw, "Custody or Visitation Interference," accessed July 17, 2015