Sorry to hear about this. So you're using the GT-P3113 (Galaxy Tab 2 7")? I see you tried setting the time manually, but have you tried to set the time zone?
I just set up my new Galaxy Tab. I love it, except the time/date function doesn't work right. It's about six hours off and when I manually try to fix it, then some of the apps *such ad the media hub* won't work because it says there are more than 2hours 10minutes between the server and device time, and it tells me to change the time. Help!