Not a gem but a console tool - ntpdate. Open a root-terminal and install it with
Code:
aptitude install ntpdate
For clock sync use
Code:
/usr/sbin/ntpdate -v pool.ntp.org
I always recommend to use UTC within BIOS and use proper settings of "tz=...." in the "APPEND" lines of '/mnt-system/boot/syslinux/syslinux.cfg' or in case of HD installation in the "kernel" lines of '/boot/grub/menu.lst'.

Have a look at '/usr/share/zoneinfo' which value may usefull for you; for example "tz=America/New_York".