Did you download the demo project or the GitHub repo? The repo has the demo as test project. It does cover dates. If your situation is not covered I will be happy to add it.
Edit: A date as axis ID value did not work at all. I guess I never tried that after the first versions and it got broken sometime ago.
I fixed it and included a demo page for it in the demo project.
I also recovered the theme.css from an older commit as it no longer contained the custom CSS classes.
It may take some time to get it on the appstore as I no longer work for the company for which it is published.
You can get the new widget mpk from the release on GitHub