Gmail stamps your messages with the date and time set in your operating system. If your messages are receiving inaccurate timestamps, you?ll need to change your operating system?s calendar properties.
Here?s how to do that in Windows:
Double-click the time in your taskbar.
Click the 'Time Zone' tab along the top of the dialogue box.
Verify that your time zone is selected. If the time zone in which you are located is not displayed, select your time zone from the drop-down menu.
Verify that the box beside 'Automatically adjust clock for daylight savings changes' is checked.
Click 'OK.'