There are two time-keeping clock's on your computer. One is hardware clock to set you bios and another is system clock. System clock is set on linux system during the boot time by copying a hardware clock time with hwclock command. To change the hardware clock we use hwclock command:
# hwclock --set --date="5/1/10 15:48:07"
The command above will change hardware clock to 15:48:07 1st May 2010. In case you need to change hardware clock to you current system clock execute a command below:
# hwclock --systohc
It also works the other way around. To set system clock from hardware clock use:
# hwclock --hctosys