There are a number of changes to timezone configuration files in Fedora 18.
Probably the biggest change is that /etc/localtime replaced /etc/sysconfig/clock and the system timezone is now configured by creating an appropriate symbolic link from /etc/localtime to the relevant timezone file in /usr/share/zonedata. This is more like what the GNU/Debian distribution and it’s downstream distributions such as Ubuntu do.
To list available timezones run the following command:
# timedatectl list-timezone
To set the system timezone, to for example Eastern Standard Time, run the following command:
# timedatectl set-timezone 'Atlantic/New York'
It just updates the link /etc/localtime to point to the correct timezone installed in /usr/share/zoneinfo/. You could do this manually from a shell if you so wished.