The J. D. Edwards samples contained in the installation of ODBCFace are using a custom function DateToJulian() that provides a conversion from Gregorian date to JDE Julian date.
The samples also contain (in the attached Visual Basic module) a JulianToDate() function that performs the opposite conversion.
You can copy these functions in your own workbooks and use them directly in the ODBCFace profile or in the Excel cells.