Being vague about the start time. "I wanted to book an hour around 3? Well, I will be in a meeting in Cambridge until about 2... and should be an hour or maybe longer to get to you... ." OK, so maybe you will leave Cambridge about 2 and maybe the traffic will be OK.... Or maybe not.
Or "are you available now? I'm just on the M1 near Sheffield. I can be with you in 20, maybe 30 minutes?"