I didn't bother to actually look at my phones before I posted. I am in the Pacific Time Zone, and my devices all display the correct time.
Perhaps you have some very old firmware or made a previous change.
Keep in mind that you must make changes via the OBiTALK dashboard, not via the device's local web page. If you do the latter, the settings will be overwritten with the OBiTALK settings on the next reboot.
See my screenshot below, for the correct settings. Use Expert mode to edit. Remove BOTH checkmarks to the right of the parameter's value to edit it. Click Submit after editing. The setting is on System Management-->WAN settings.