XCOPY /d is documented to take a date in the form dd-mm-yyyy but I can't find any mention of similar support for time.
Is there (or a workaround even) or do I have to download another command line tool for winxp?
There's no way to include time as a criteria in XCOPY. This is true for ROBOCOPY as well, even though it has many more configuration options than XCOPY.
The XXCOPY application will do what you ask -- but as you say, this costs money (for commercial uses, anyway).
http://www.xxcopy.com/xxtb_001.htm - search for "/DA:".