Ever noticed that many groups have an insidious culture of running late for meetings? It seems almost that the bigger the organisation the worse the problem.
Of course there can be a number of contributing reasons, but one big one is very simple and ragingly obvious - people don't allow themselves enough time to get there.
If you work in any organisation bigger than about 4 or 5 people all in the same room, you'll have walking time, quite aside from all the other factors. Add a few floors or different buildings to travel to and from, and no one is surprised when people run late. Then, insidiously, it becomes the norm to start late and run over time. I don't believe it's ever acceptable (unless there are very unusual circumstances).
Trouble is, not only is there the travel or walking time, but what about toilet time, 'gather my wits' time, the quick and urgent phone call, the last minute 'please help' from a colleague as you head out the door, the coffee and water time when you get to the other end? It's as if most people go into a time warp and blank out reality. Just notice - if even one prompt person is waiting, the organisation's resources and money are being wasted. Try doing a cost analysis on that in any decent sized organisation, and you'll be horrified at the price tag.
Here's a way to deal with this issue. As soon as you accept a meeting, block out the travel time and 15 minutes either side of it. This will act as a prompt when you're tempted to slide in 'just one more thing'.