You don’t mention what client you’re using.
If you’re using a mail client on your local machine, times should be displayed correctly with your machine’s local time. If you’re using webmail, you can set the time zone under:
“Options -> Personal Information -> Your Current Timezone”
If you’re using Pine on a shell machine, you need to set the TZ variable appropriately.
The Received headers added by our mail servers will show the time in our local time (Pacific) along with the offset from GMT… however the display in the message index should be based on your local time.