System admins have the ability to manually set an expiration date for a record type's workflow step.  To do this, you will navigate to this document step in the record type's settings and you will see that whether the document expires is either set to
yes or 'no.'

If you choose for the Expires field to say "Yes," you will then see a dropdown menu where you can choose either "Expires After" or "Expires On."  If you choose "Expires after," you will have the option to choose if the document expires after X amount of days, months, or years.

If you choose "Expires On," you will be able to choose a specific expiration date for this document.

You also have the option to click on Advanced Settings, which brings up the ability to choose the minimum amount of time that the document will be valid for.  In the second screenshot below, you'll see a guiding prompt that pops up if you hover your mouse over the question mark where you choose your minimum document validity timeframe.  Please note that if you do not manually choose a minimum document validity timeframe, the document will automatically expire as the next occurrence of the default expiration date.
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