The real solution to this problem, sorry I stopped typing above, is to disable iMessage on your phone and have your phone connected to your mac, sync with iTunes, but do not back up. Turn iMessage back on, re-sync your phone. The only thing time zones will do is send you the message later than you should receive it instantly, but that is also an inconvenience, so do make sure your time zones are correct, but it's a useless response to tell someone to do that if they haven't traveled outside the country and their time is set to "automatically update". So, unless you changed your clock and entered an area where there was no cell service or wi-fi to automatically update your clock, this will not solve your problem. Again, Turn off iMessage on your phone, Sync your phone to your iTunes account, let it finish syncing, eject your phone, turn on iMessage, resend your phone, a message SHOULD come up that your phone number would like to use the iMessage account on your Mac...