BaseForm.setTimezone

Sets the time zone for the current form, service or workflow process. All dates and times displayed on web pages will use this time zone. It is recommended that this method is called to set a time zone prior to setting values on any fields of type date, time or datetime.

Examples:

 form.setTimezone("America/Chicago");
 form.setTimezone("America/Los_Angeles");
 form.setTimezone("America/New_York");
 form.setTimezone("Europe/Paris");
 form.setTimezone("Etc/GMT");