Most beginning researchers frequently ask, "How do I know when I am done?"
Here are a few good indicators that you've reached the end of your research project:
What if you're not finding authorities that address your research issue?
We usually tell students that if research hasn't yielded any results after 30-45 minutes, it may be time to reevaluate your research strategy.
Think comprehensively and creatively. Research broader rules, analogous facts or doctrines, and⁄or the law of other jurisdictions.
Make sure you are:
Consult a librarian.
What if time is running out and you still have intriguing leads to follow?
Quickly survey the major authorities bearing on your issue.
Prepare an interim report that describes the conclusions you've reached so far and your plan for further research.
For more on when and how to wrap up your research projects, take a look at these articles.
Some of the details may be a bit dated, but the overall advice is still sound.