From Changing the timezone, date, and time.
The date and time can be changed directly to the hardware clock and then used to update the system clock.
> hwclock --show
Tue Nov 4 22:13:40 2003 -0.684660 seconds
> hwclock --set --date"02/19/2003 15:00:00"
> hwclock --show
Wed Feb 19 15:00:06 2003 -0.755080 seconds
> date
Tue Now 4 22:15:06 PST 2003
> hwclock --hctosys
> date
Wed Feb 19 15:00:34 PST 2003
