SQL Server 2022

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DECLARE @Stamp BIGINT = 638488466706836320

SELECT
    -- Maximum accuracy
    DATEADD(day, @Stamp / 864000000000,
       DATEADD(second, @Stamp % 864000000000 / 10000000,
           DATEADD(ns, @Stamp % 10000000 * 100,
               CAST('00010101' AS DATETIME2)
   ))) AS ConvertedDateTime1,

-- Reduced millisecond accuracy
    DATEADD(day, @Stamp / 864000000000,
        DATEADD(millisecond, @Stamp % 864000000000 / 10000,
            CAST('00010101' AS DATETIME2)
    )) AS ConvertedDateTime2,

-- Adjused for use with a 1900-01-01 reference date (1/300 second accuracy)
    DATEADD(day, (@Stamp - 599266080000000000) / 864000000000,
        DATEADD(millisecond, (@Stamp - 599266080000000000) % 864000000000 / 10000,
            CAST('19000101' AS DATETIME)
    )) AS ConvertedDateTime3,

-- Convert to text "yyyy-mm-dd hh:mm:ss" and strip punctuation
    REPLACE(REPLACE(REPLACE(CONVERT(VARCHAR(23),
        DATEADD(day, @Stamp / 864000000000,
            DATEADD(millisecond, @Stamp % 864000000000 / 10000,
                CAST('00010101' AS DATETIME2)
        )),
        120), '-', ''), ' ', ''), ':', '')
        AS ConvertedDateTime4

ConvertedDateTime1	ConvertedDateTime2	ConvertedDateTime3	ConvertedDateTime4
2024-04-16 06:44:30.6836320	2024-04-16 06:44:30.6830000	2024-04-16 06:44:30.683	20240416064430