Going to be the contrarian since everyone else is giving the answer you probably expected.
If it is important then I will be there on time. Not 30 minutes early. Maybe 10, but being excessively early is just a waste of my time and I’m not in a contest to see who can be there the earliest.
Most of the time however I find that people give fake importance to a lot of events. There are so many things that simply won’t matter in life or that we’ll forget about by next week. The types of people that would rather insult or completely demean or belittle someone over being 5 minutes late are my least favorite people on the planet. Very few things are that important.
It takes more time and effort to complain than it does to be understanding and realize that most of the time the someone is really not a life or death crime. I live on a schedule but things happen and if someone treats me poorly over a small time issue it becomes their problem.