Difference Between First Bill, Second Bill & Last Bill

Anonymous 

If you were to use DAX and a calculated column here below is the DAX you could use:

TimeDiff =
VAR mobileNum = [Mobile #]
VAR billDate = [Date]
VAR billTime = [Bill Time]
VAR firstBillTime =
    CALCULATE (
        MIN ( [Bill Time] ),
        FILTER (
            TableBills,
            TableBills[Mobile #] = mobileNum
                && TableBills[Date] = billDate
        )
    )
RETURN
    IF ( firstBillTime = billTime, TIME ( 0, 0, 0 ), billTime - firstBillTime )

However, passing by Power Query might be a better approach to add a column

Let us know if that works for you

David