Please enter a time unit of measure

What causes this issue?

You have specified a period before or a period after, without
specifying a time unit of measure. The system cannot therefore
calculate the start and end dates of the averaging period.

System Response

The system requires you to enter a time unit of measure.

How to fix this error?

Enter a time unit of measure if you want to use the period before/after
functionality.

Error message extract from SAP system. Copyright SAP SE.