"Let's wait a few minutes for folks who are still joining..."
Translation: remember when you were taught to be punctual (or even early) for things, especially business appointments? Recall how you were told it would make you more professional and that it would show you care about details and other peoples' time?
Somewhere along the way, we put "maximum participation" ahead of valuing time and consideration for people who take the time to be on time. Airlines figured it out: stragglers cost everyone time and money. So if the gate doors close, you miss your flight. Webinars and group meetings have eroded into a "we're going to wait until it feels like enough people are here" behavior, penalizing those who value punctuality and preparation and rewarding those who felt like other commitments were higher priority.
It doesn't have to stay this way.
"This meeting will begin punctually" - that's all you have to say. Eventually you won't even need to say it, it will just become self-evident to your team.
Try it within your team and dare to have the courage to do it when you undertake your next sales webinar. "We're going to start promptly" is going to be well received by people who take the time to show up on time, and people who are late will eventually learn that "waiting for a few more minutes" penalizes everyone EXCEPT the people who didn't take more time to prepare or test their connection.
Try it in your organization. If it fails, send us an email and explain why. If it succeeds, share the idea so we can normalize punctuality again.