Some clocks can be programmed to make noise nowadays at a certain time.
It's tough to fight this, because the person you're fighting is yourself, and you're just as smart as you are, so you can't outsmart or trick yourself.
Sometimes, some technique will work for a day or two, but the brain adapts very quickly and learns how to get around it.
I'm very absent-minded and frequently forget things like eating and cleaning, but out of respect for other people, I frequently take notes and set alarms, which at least helps me stick to agreed schedules.
Another useful way to manage it is to schedule things loosely when possible. Agree to meet at some point in the span of an hour under circumstances where neither party will be bored waiting. For example, invite the other party over an hour before going to a see a film.