follow these steps
adding all the above steps together
eval DateMin=strptime(DateMin, "%Y-%m-%d %H:%M:%S"), DateMax=strptime(DateMax, "%Y-%m-%d %H:%M:%S") | eval Diff=round((DateMax-DateMin)/60,2) | where Diff > 6
you can merge them to a single eval. But I though this will give you good clarity.
Hope this helps