The following linux commands will allow you to change the time zone on your CoreOS Linux. Currently, the time zone is set to UTC:

coreos ~ # date
Sun Aug 9 09:34:17 UTC 2015

By using the timedatectl list-timezones command you can obtain a list of all available time zones:

coreos ~ # timedatectl list-timezones

Feel free to pipe the STDOUT of the above command to find your desired timezone. For example here we are searching for sydney:

coreos ~ # timedatectl list-timezones | grep -i sydney
Australia/Sydney

Finally, use timedatectl command to set yur new timezone:

coreos ~ # timedatectl set-timezone Australia/Sydney

Test you new time zone settings:

coreos ~ # date
Sun Aug 9 19:35:54 AEST 2015