If the time displayed on your Gmail messages does not match your system clock, there may be an issue with the time zone listed in your Google account settings. Here's how to set your Gmail account to the correct timezone.
Change a Gmail Timezone
Sign into Gmail and head to your account settings. Find the section labeled Personal Settings and click on Edit.
Scroll to the Time Zone field, and choose the time zone that matches your location.
Click Save to apply your settings.
You can verify that your timezone was set correctly by simply signing out of Gmail and then logging back in.