Of course, "showing up 5 minutes late" isn't relevant if you've pre-selected each other ahead of time, you know?

Not necessarily! I had a situation where I'd pre-planned to work with someone who forgot they said they were gonna work with me, and "panic" does not even BEGIN to describe the resulting scramble. I was in the middle of Nowhere, Indiana with one come-and-go bar of 3G service on my phone and no reliable WiFi.