Re: Difference between dates in the same column

,

According to your description, you could add a calculated column as follows.

Duration Column = 
DATEDIFF (
    Table1[Action Date],
    LOOKUPVALUE (
        Table1[Action Date],
        Table1[Req No], Table1[Req No],
        Table1[Apr Seq No], Table1[Apr Seq No] + 1
    ),
    HOUR
)