In Windows and Ubuntu dual-boot machine,you may find the two system times are different.My Windows time is always 8 hours ealier than Ubuntu 9.04 time.But after Ubuntu 9.10 installed this error disappear (maybe ubuntu 9.10 has this error fixed).
The reason why the two times are different is that Windows uses BIOS clock as its time clock and Ubuntu display BIOS time plus Greenwich Mean Time.For example,Beijing is GMT+8 so Ubuntu time clock display BIOS time plus 8.

Commonly,BIOS clock shows the real time,so we can try following to fix this problom.
In Ubuntu,open terminal from Applications->Accessories menu and type:

sudo gedit /etc/default/rcS

find this section “UTC=yes” (without quotes) and change it to “UTC=no” (without quotes),save and reboot.