I believe it's about the common case of two events sharing a single (infinitely small) point of time: meeting A from 3 to 4, followed by meeting B from 4 to 5.

I believe it's about the common case of two events sharing a single (infinitely small) point of time: meeting A from 3 to 4, followed by meeting B from 4 to 5. Those two time periods do overlap mathematically, but not physically: they share the common point of "4", even if that point has duration 0. I know the iCal standard goes into this for a bit.