Date time index.indexer between time
- [ ] closes #xxxx
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

Please take a look and let me know if things look fine, I'll make a whatsnew entry then :)

This PR has been made as per [this](https://github.com/pandas-dev/pandas/pull/43248#discussion_r701003907) suggestion by @attack68.