So that the time and date of messages and other content your post is correct based on your location, it's important to set your timezone in your personal profile.
To do this, simply go to My Account (this appears under your name on the left hand side when you are logged in).
Then click on the Edit tab at the top and scroll down until you see "Locale Settings". Here, just choose the time that is right for your locaion. Click Submit, and you're done!