Here is an excerpt from Qwiklabs Games help page:
How points are calculated
Each game has multiple labs, listed in subject groupings for ease of viewing.
You earn points by completing each lab's required steps and finishing the lab quickly.
- Required steps are counted within each lab, using Activity Tracking.
- Bonus points for speed if you finish all required steps in a lab before the timer runs out:
- The lab timer shows the maximum time you have to do the lab. The timer starts counting down when you click Start Lab, and times out when the timer reaches zero. If you finish the lab before the timer reaches zero, be sure to click End Lab to earn bonus points for speed.
- The time between when you finish one lab and start another lab does not affect your score.
Your score is calculated by combining the scores of all the labs you've done. So to maximize your points, do more labs!