Assuming you and everyone you’re greeting didn’t need to sleep, eat, drink or do anything other than saying/hearing “Hi” but death from old-age still applies, but only to you. For reasons.
I don’t know. I’m not showing my working out, this is showerthoughts not ‘math genius’ don’t @ me.
I think if we assume you will live till you’re 90 and the population of the earth remains at 8 billion then you get about 0.36 seconds per person.