I use the classic layout because my connection sucks... but right after you log in, on the left, a button should appear that says, "Options". From there, select, "Personal Information" (or something like that). You can change your region and such here... It's the only place I know of that allows you to change anything related to timezones.
If that doesn't work... is the clock on your computer correct? Some sites will base sent times from your computer's clock.