If have something else scheduled, and it's not this work related, it's my other work related, I will be explicit and say that I don't have much of a window for lateness and to prepare ahead of time, they have been great about it. On the flip side, if I have time and they are running late, I just tell them to relax, don't speed or get into an accident and get here when they can...no problem.

I am a stickler for punctuality  but do see the unforeseen cropping up. Only on I think about 2 occasions  have I had to cancel a guy that was running way too late because I had to be somewhere else to be.