Request DAX For Ranked Order Date Tracking for Different Orders on Same Date

Hi,

I am not sure if I understood your question correctly, but please check the below picture and the attached pbix file.

Order Number calculated table = 
VAR _maxrowcount =
    MAXX (
        ADDCOLUMNS (
            VALUES ( Sales[Customer] ),
            "@rowcount",
                COUNTROWS (
                    WINDOW (
                        1,
                        ABS,
                        -1,
                        ABS,
                        Sales,
                        ORDERBY ( Sales[Index], ASC ),
                        ,
                        PARTITIONBY ( Sales[Customer] ),
                        MATCHBY ( Sales[Customer], Sales[Index] )
                    )
                )
        ),
        [@rowcount]
    )
RETURN
    SELECTCOLUMNS( GENERATESERIES ( 1, _maxrowcount, 1 ), "Order Number", [Value] )

order date tracking: = 
VAR _t =
    GENERATE (
        VALUES ( Sales[Customer] ),
        VALUES ( 'Order Number calculated table'[Order Number] )
    )
VAR _result =
    ADDCOLUMNS (
        _t,
        "@orderdate",
            MAXX (
                INDEX (
                    'Order Number calculated table'[Order Number],
                    Sales,
                    ORDERBY ( Sales[Order Date], ASC, Sales[Index], ASC ),
                    ,
                    ,
                    MATCHBY ( Sales[Index] )
                ),
                Sales[Order Date]
            )
    )
RETURN
    MAXX ( _result, [@orderdate] )

diff vs previous measure: = 
VAR _currentorderdate = [order date tracking:]
VAR _previousorderdate =
    CALCULATE (
        [order date tracking:],
        OFFSET (
            -1,
            ALL ( 'Order Number calculated table'[Order Number] ),
            ORDERBY ( 'Order Number calculated table'[Order Number], ASC )
        )
    )
VAR _condition =
    INT ( _currentorderdate <> BLANK () && _previousorderdate <> BLANK () )
RETURN
    DIVIDE ( INT ( _currentorderdate - _previousorderdate ), _condition )