well if you set fixed_date="20030205 22:00:00"

when you issue select sysdate from dual you will always see that, slimdave already pointed that out

if you then get rid of parameter you get the old supposed wrong date again

quoted from doc:
FIXED_DATE lets you set a constant date that SYSDATE will always return instead of the current date. This parameter is useful primarily for testing. The value can be in the format shown above or in the default Oracle date format, without a time.

useful for testing, nothing else nothing more

Oracle uses date from OS, it's internal clock is SCN not date