To enable the stealth mode, like PMTPOSD2's, start the new CLOCK.EXE (English) or CLOCK_NL.EXE.EXE (Dutch) with any single parameter. The word "stealth", for example. Then the clock should no longer appear in the Task List nor the eCenter.
AFAIK a claim, the clock will store its current window position when you manually close it, may not be true. Or may not be true anymore, at least if the open sourced release is anything to go by.
To enable the stealth mode,