The jconsole manual leads to the right solution: just format the time column appropriate.
If your locale like mine doesnt use "." (dots) as decimal separator, you have to do a additional step(s). In Excel 2003 before you import first rename the file extension to ".txt". Then for a german localized Excel you have to choose for the time column the "." as decimal separator and choose the ' (single quote) as 1000er separator. While you import the file left the time column format as "standard".
Then I have choosen format userdefined with the format string "TT.MM.JJJJ hh:mm:ss".