What is the best example of potential energy?

When an archer pulls back the bowstring, some amount of elastic potential energy is gained by the flexible limbs of the bow. The more an archer pulls back, the more potential energy will be gained by the limbs of the bow due to stretching. When the bowstring is released, the arrow moves forward very quickly. What happens here is that the potential energy that is gained by the bow due to stretching is being quickly transferred to the arrow in the form of kinetic energy, and so, it moves forward.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.