On the SUSE Linux discussion list I read the following article: [SLE] Installing 9.3 - "time is in the past" ?????. Apparently YaST, SUSE's configuration and installation tool, figured out that the time was way off and told the user about it but the user could not change the time in YaST. I tried to reproduce this and got the same message but could change the time without problems, so no idea what went wrong.
The funny thing was that my BIOS allowed to set the year 1981 but once I rebooted, the BIOS told me that I had to check "date and time". Checking it back it showed the year 1988, which neither worked. So I had to use the year 2000 to get through the BIOS. Seems my computer makes similar checks like YaST.