Starting and ending meetings on time is a sign of respect.
If you start or end a meeting late, apologize to the others and provide an explanation. Apologize like you mean it. If you find yourself constantly apologizing for being late, you don’t mean it. You simply think that your time and activities are more important than other people’s.
Realize that there is nothing magical about a 30-minute or a 60-minute meeting. While it might be convenient to start meetings at the top or the bottom of the hour, they don’t need to end there as well. Schedule 20-minute and 45-minute meetings, stick to the timing, and give everyone a few minutes before their next meeting – so that they can be on time.