BUG: GroupBy.apply with Grouper and NaT
- [ ] closes #xxxx
- [x] tests added / passed
- [ ] 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
- [x] whatsnew entry

Inching towards getting rid of redundant index-like attributes
hmm some failing tests fixed ex windows timeout