The plugin info says:

References %1, .. %n are allowed, and will be replaced by the groups matched by the Regex. %0 is the whole match.

The documentation says:

If the text is "Total time: (\d+)" and the script is "script.sh", then if the log contains a line "Total time: 10", the "script.sh 4" will be called.

Neither works. When using %0, %1 etc., %0 becomes the path to a temporary batch file that seems to be used to call the script, e.g., C:\Users\<User>\AppData\Local\Temp\hudson2844785260200969554.bat.