When it comes to dates, or really any appointments, punctuality is often taken as a sign of respect. You respect the person you're meeting, you respect their time, and you acknowledge that they have other things to do.
Same goes with dates. It's nice to show up a couple of minutes early to figure out the place and find your date if you're meeting somewhere new. Even if you're going to a familiar place, like your date's house, arriving a little early shows interest and that you care.
If you're getting late (there are some inevitable occasions where you may have an emergency to deal with), CALL! Let the person know, with as MUCH time as possible. Hopefully, they won't be stranded and waiting for you, bored.