How To Determine Date Format to use in CSVs

Migrating content from SharePoint site via Source CSV plugin and Migrate Plus. I am new to Drupal. Does anyone know how I determine what date format to use in my CSV?

Have tried a few combinations but none have worked. Here is the yml relative to date (field_publish_date is a Date type):
‘field_publish_date/value’: PublishedDate

And here are a couple I have tried (from SharePoint):
9/22/2014 1:56:00 PM
2014-09-22T13:56:15Z

Any help will be appreciated.

bob

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