Use a clock.
For the love of all things organized.
It's amazing to me how many people actually think that sun revolves around them. Newsflash folks: even Galileo figured out that the earth -- and all things on it -- revolve around the sun.
Let me go back a bit. Recently I've been exposed to a particular person who thinks that time is something that answers to them, instead of the other way around. So when they asked me to help them out in a pinch, I quickly learned that how that really works is that I am at their whim until they decide to "let me off the hook" as it were. I'd rather not elaborate.
No, I will. I decided to help this person by watching their kid. But they never showed up to reclaim the kid until hours -- 2, 3, 4 -- after they got off work. No phone call, no explanation.. sometimes an excuse or two. Usually I'd call their phone to get the voice mail. Sometimes they'd call back and say "I'm five minutes away" and show up 45 minutes later.
Do I need to tell you how sick I got of it? Forget the fact that it's chaotic for the kid, and not at all an example worthy of setting... but it annihilated my schedule, elevated my stress, and to call a spade a spade -- it pissed me off.
So I said something about it. Blamed it all on me even. Said "I didn't function well being left out on a string like that. Didn't know how to plan for anything, couldn't make any plans of my own, and that I didn't know what to tell the kid when he asked when he could go home. Please start calling me. Just a call. Just let me know what's going on; let me know you're alive at least." So I've almost started getting calls. At least they answer the phone when I call now. "Five minutes" still means 45 minutes. And the 3-4 hours has shrunk to 1/2-2 hours. It's better. It ain't great, but it's better.
I'm thinking of getting them a watch for Christmas so they can better tell time for their next sitter. And maybe a scale model of the universe... with the sun in the center.