Lateness is a bad habit. While there are occasions when most of us will run late once in a while, it is an exception. When you think about your group, the same people are consistently late. Once in a while, they may come early because they forgot to change their clock or something, but for the most part, they are consistently late. It’s a bad habit.
If you want to reinforce their bad habit, then hold off on starting the meeting until everyone has arrived. The latecomers will understand that the whole group will wait for them, so there’s no need to be on time. If you want the latecomers to think about changing their ways, then start the meeting on time. When they walk in and the meeting is already started, they will say, “Oh, excuse me, I’m sorry for being late.” That little bit of awkwardness or embarrassment just might motivate them into being on time next week.
Here’s the flip side: if you wait for people who are always running late, what are you saying to the group members who show up on time? By waiting for latecomers, you are dishonoring the people who cared enough to show up on time. My rule of thumb is this: respect those who are on time by starting the meeting. Embarrass the latecomers. (I’m a Kansan. I can’t help it.) But test me on this. If your group starts at 6:30 and you announce at 6:30 that you are no longer going to wait for the late people, but that you are going to start on time from now on, listen for the cheer.