CC, I should have added that there's the first rush which wipes out a load from around 400m.
Most are simply running as fast as they can go at any moment in time. The reason they come back at around ten minutes is their blood lactate levels have hit maximal levels.
That's why I catch so many and pass them after that time.
If a road racer wants to hit optimum average pace for the entire race, they have to set off at what feels like 3/4 pace, and be prepared to let all and sundry go ahead of them, sometimes almost out of sight.
That takes confidence and nerve.
I don't do 'banking time', because it yields an inferior result to correct pacing. It's physiologically speaking, inefficient.