Plotting Calculated Weekly Revenue and/or Return % between BillStart and BillEnd Dates.

Hi DataUsurper ,

Please try the optimized way.

Table = 
VAR a =
    CALENDARAUTO ()
VAR b =
    SELECTCOLUMNS (
        'Order',
        "id", 'Order'[MAIN_ORDER],
        "product", 'Order'[MAINCODE]
    )
VAR k =
    ADDCOLUMNS (
        FILTER ( CROSSJOIN ( a, b ), WEEKDAY ( [Date], 2 ) = 1 ),
        "filter",
        VAR ship =
            CALCULATE (
                MAX ( 'date days'[SHIP_DATE] ),
                FILTER ( 'date days', 'date days'[ORDERID] = [id] )
            ) - 7
        VAR returndate =
            CALCULATE (
                MAX ( 'date days'[RETURN_DATE] ),
                FILTER ( 'date days', 'date days'[ORDERID] = [id] )
            )
        RETURN
            IF ( [Date] >= ship && [Date] <= returndate, 1, 0 )
    )
RETURN
    FILTER ( k, [filter] = 1 )

Days in use2 = 
VAR st =
    CALCULATE (
        MAX ( 'date days'[SHIP_DATE] ),
        FILTER ( 'date days', 'date days'[ORDERID] = 'Table'[id] )
    )
VAR returndate =
    CALCULATE (
        MAX ( 'date days'[RETURN_DATE] ),
        FILTER ( 'date days', 'date days'[ORDERID] = 'Table'[id] )
    )
VAR maxdate =
    CALCULATE (
        MAX ( 'Table'[Date] ),
        FILTER (
            'Table',
            'Table'[id] = EARLIER ( 'Table'[id] )
                && 'Table'[product] = EARLIER ( 'Table'[product])
        )
    )
VAR mindate =
    CALCULATE (
        MIN ( 'Table'[Date] ),
        FILTER (
            'Table',
   'Table'[id] = EARLIER ( 'Table'[id] )
                && 'Table'[product] = EARLIER ( 'Table'[product])
        )
    )
RETURN
    IF (
        [Date] = mindate,
        DATEDIFF ( [Date], st, DAY ),
        IF ( [Date] = maxdate, DATEDIFF ( [Date], returndate, DAY ), 7 )
    )

Revenue2 = 
VAR suma =
    CALCULATE ( SUM ( 'Table'[Days in use2] ), ALLEXCEPT ( 'Table', 'Table'[product], 'Table'[id]) )
VAR val =
    CALCULATE (
        SUM ( 'Order'[  ITEMTOTAL  ] ),
        FILTER ( 'Order', 'Order'[MAINCODE] = 'Table'[product] )
    )
RETURN
    DIVIDE ( val, suma ) * 'Table'[Days in use2]

Pbix as attached.