Final answer:
The P wave in an ECG represents the depolarization of the atria and occurs approximately 25 ms from the start of the wave to when the atria begin to contract.
Step-by-step explanation:
The P wave in an ECG represents the depolarization of the atria. It is a small wave that is generated by the electrical activity of the atria as they contract. The time for the P wave is approximately 25 ms from the start of the wave to when the atria begin to contract.