Just over 227 years, that was what I had calculated for how long it would take to say hello to and shake the hand of each person alive right now. Figuring one person per second, 24 hours a day and there being roughly 7 billion people alive. With the same one second required to say hello to and shake the hand of someone, one could great a 40,000 person town in a bit over half a day.
The best that most of us can to is to help those that we are around directly. That’s how one impacts reality.