Hi @Harry N Nomikos ,
Here is the formula of calculated column:
=IF(AND(TestedDate>=DATEVALUE("6/5/2023"),TestedDate<=DATEVALUE("6/30/2023")),"2023 EOFY Blackout Date","")
TestedDate is the name of the date and time column, In the above formula you need to replace the name with the name of your date column.
Fill Formula to the position as shown (Result is the name of the calculated column).
The demonstration results are as follows. In addition, in the list of SharePoint, the date format is month/day/year.
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