You need to set this option only if your webserver resides in a different timezone from yours. If you cannot find your timezone in the drop down list, you can just specify the time offset from your localtime to the time on your webserver, in format HH:MM if your time is ahead of the server time or -HH:MM if your time is behind. The current time on your webserver should be printed on the form.
Timezone info is used to control audio, video and email reminders. If you're not going to use these reminding services, you don't need to set this option.