When you fill out your profile, you need to select your time zone in order for your posts to display the correct time stamp. All time zones are selected based on Greenwich Mean Time. You add or subtract from GMT to get your time zone.
Eastern Standard Time = GMT - 5 hours
Central Standard Time = GMT - 6 hours
Mountain Standard Time = GMT - 7 hours
Pacific Standard Time = GMT - 8 hours
Or, you can follow this link to find your time zone
Items like this can be updated in your profile at any time.