I'd like some advice on how to improve my meetings, and the meetings run by my directs with customers.

From the podcasts, I understand the importance of starting meetings on time and ending on-time, but I have some customers in particular that make it incredibly difficult.  For example, 80% of my staff are remote on-site at customer facilities.  I have one customer we have weekly meetings with, and he does not allow us to control the meeting invite.  Often he has a conflict with the room he booked, or the wifi, or the projector, so my direct can't begin the meeting on-time.  I've worked with my direct on how to take control of what she can, like sending an agenda and particular phrases to move the meeting along when we get stuck, but I feel stuck in coaching her since many of the things are out of her control.

Overall, most of my customer meetings start late because the external participents call in/show up late.