Make sure you have:
- Registered a Google place and associated it with your website (if not, you can do it here: https://www.google.com/business),
- In Nightwatch, you entered the exact place name in “Local Place name” in the URL's configuration.
You can do it if you select a URL in the sidebar and go to its SETTINGS below.
Additionally, you may find our Ultimate Guide to Local Tracking helpful.
Nightwatch updates rankings every 24 hours, and the pages are picked up as soon as your website starts to rank in the top 3 places in the Local Pack.