No matter what you do, you cannot force your students to always put you at the top of their priority list. It may seem like a surprise to you, but most of these students feel like they're being burdened a lot because they had to keep up with school, their families, their social lives, et cetera. And sometimes their priority lists are not that slick and solid anyway! One day they can stick to it and on another they can easily veer away at the sight of an upcoming party advertised at bright custom feather flags.

Meaning, if they don't come on time for your class, most likely they were attending to something that they deem more important that your class (or your feelings). Just let them be. At the end of the day, when you give out quizzes and exams and they don't give you the right answers, they might start to be challenged to come early. After all, nobody wants to fail.

On the other side, don’t overconsider also. Follow your school’s rules in absences and tardiness and just tell them that those things are things which you can really do nothing about. If they surpass the maximum number of allowed absences, you can give them a failing mark (debarred). If they’re nearing that threshold, you can give them a warning or two. That’s that right thing to do.

What is important is that you do your job well and that you do everything in your power to help them grow as individuals, not merely students. What you teach them is professionalism and courtesy in general, and punctuality is a very important factor of those principles. So relax. You don't need to remind them as frequently as purposively as those corporate street light banners.