CoachA moment is one point of the day: the moment the bell rings. A duration is the stretch of time between two moments: from the bell to the end of the lesson. Moments answer when?; durations answer how long?
Examples
Example 8.3 (When or how long?)
“The film starts after dinner” talks about a moment. “The film lasts as long as two lunch breaks” talks about a duration. “My birthday is in spring”: moment. “The holidays felt so short”: duration — and this chapter is mostly about durations.
Example 8.5 (The sand timer)
A sand timer is a little glass with a narrow waist: the sand always takes the same duration to pour through. That makes it a referee. Brushing your teeth against the timer: the sand ran out first — brush longer! A song against the timer: the song won. So the song lasts longer than the tooth-brushing, though they never raced each other directly.