Approval flow with custom attributes

Summary:

We have the below requirement-

System must route the Resignation request to a BU Head , if the Termination Date generated by the system which is (Notice Period Days+Notification Date) minus Last working Date requested by employee in the Termination/Resignation Page is greater than X days. The Approval configuration console doesn’t seem to have the ability to frame such condition. 

Attached is the screenshot of the Approval Configuration-

Can someone pls suggest if there is a way to achieve the business reqmts?

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