e-mail is time stamped yes, but its time stamped several times so unless you look at the full smtp headers the time it arrived at your mailbox or mail provider can still be different than when it was sent.
I run into that a lot because my e-mail is trhough a small company I found in AZ and I'm in OH so the time zones and time stamps are always crazy, the times that show on on the mail someone recives from me will show some crazy time.