Help with "informal" meetings

I've just experienced a problem and would like some input.

There is a recurring meeting that involves demonstrating software to some stakeholders (internal customers).

At first, I didn't schedule a recurring meeting, because I expected people to just stop by every other day (as was discussed).

When they didn't show up, I scheduled a meeting.

Today, one person showed up 5 minutes late; another showed up 10 minutes late. One person didn't show up at all. No one (except me) showed up on time.

No point starting on time, right? What would you do? Chase everyone down? Start when the first person shows up (who, by the way, was the least "important" attendee).