Formula Help - Return Min if no Null values present

I have 2 Min formulas where when one is Null in another formula, it returns the other value.

I need the second Min formula to only calculate when a specific date field has a value ("[End Date (Report Specific)]").


Delivery Deadline Calc1 Formula
Min ([Delivery Deadline1], [Delivery Deadline2])

Delivery Deadline Calc2 Formula
Min ([Delivery Deadline3], [Delivery Deadline4])


Report Deadline Formula
Nz([Delivery Deadline Calc2], [Delivery Deadline Calc1])