How long should the watch last?

The answer to this question is very simple. As long as possible! The longer you observe, the more meteors you will see, and therefore the more certain your results will become. Furthermore, the part of the activity profile you cover becomes wider. Perhaps if you stop too early you will miss the best activity. Therefore, you should continue your observations as long as circumstances or fatigue permit. The minimum watch length which is useful is 1 hour.

Note that you should note time labels at least every 15 minutes. During high activity even 5 minutes or less.