Except for one or two stages this year*, the BOTD (Breakaway of the day) came after a flurry of attacks in the first 10k of the race. One after the next. RadioTour is constantly updating us as to who is in the breakaway. We write them down on a white board and then quickly erase them when they get caught. Some get up to a minute lead, but then they get reeled in.
She reads the numbers off so that the team directors know who's in the break. Everyone has a roster taped to their dash.
While the attackers are trying to get a breakaway started, plenty of lesser guys are stopping to pee. usually in small groups. And the racing continues at the front. But when the big names (Yellow Jersey, Wiggins, Cavendish, etc) stop to pee, the racing is shut down, and whatever breakaway is up the road at the time is given a huge bonus. That's what this clip demonstrates.
The Yellow Jersey doesn't necessarily wait for a quiet point in the race. He creates it.
*San Jose for sure. The very first attack came in the first Km and they stayed away for most of the day.