Closes #36541 (BUG: ValueError: cannot convert float NaN to integer when resetting MultiIndex with NaT values)
- [x] closes #36541
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I might need some help regarding the build error (Arm64, Xenial, Py3.7). Seems like there are some files missing, but I’m not sure what I could do to fix that...? pls merge master as well ready to merge @jreback thanks @ssche very nice!