calculate Difference from previous date

This expression works in a calculated column to get your desired result.  Replace "Data" throughout with your actual table name.

Previous Value =
VAR thisdatetime = Data[DATES]
VAR prevdatetime =
    CALCULATE (
        MAX ( Data[DATES] ),
        ALLEXCEPT ( Data, Data[name] ),
        Data[DATES] < thisdatetime
    )
RETURN
    CALCULATE (
        MIN ( Data[VALUES] ),
        ALLEXCEPT ( Data, Data[name] ),
        Data[DATES] = prevdatetime
    )

If this works for you, please mark it as the solution.  Kudos are appreciated too.  Please let me know if not.

Regards,

Pat