My mom, my gramma, and my aunt are the "problem children" when it comes to arrival times. Now that my gramma travels with either my aunt or uncle she arrives in a more timely fashion though.
The problem is not anyone arriving late though, the problem is that if any one of them is less than a half an hour early they think they are running late! In truth my mom is the worst of the bunch. She always had us arriving at least an hour early to anything, and has not changed one smidge over the years.
I have taken to asking them to show up at least a half an hour later than I want them, and if my mom says she will be here at noon, I start looking for her at 10:30 or 11.
NightMist