When there's a buzzer that will sound, you need to maximize the points you collect before time is up.
This happens for example in test scenarios.
Get as many points on the board as you can before the buzzer sounds.
Most people default to going deep on each problem, keeping it loaded up in memory so they can effectively make progress on.
But this is a bad strategy in most test taking scenarios.
Some problems will be much harder than others but still give you the same number of points.
You should focus on the points that are easy for you to get.
So go breadth first so you never get stuck without points.
You have to bottom out a line of analysis to get the points, so depth takes longer.
Depth is only worth it if it gets you more points.