In order to bring in data from Google Sheets the date has to be formatted in one of the accepted date formats provide by Google.
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To view the accepted formats click Format--> Number-->More Formats-->More dates and time formats...

If you are unable to get your date format, that could mean it is a string. You can use =DATEVALUE to try and convert.

Quarterly data is not an actual "date" in the eyes of Google or many databases. You'll need to still format the quarter as a date.

Here is a quick tutorial video to give you a hand: