If you fell for that you bricked your phone.
What actually happens if you decide to set your iPhone back to January 1st, 1970? It’ll brick your device, and there’s no fix for it: even Apple’s own Geniuses can’t figure out how to fix it, and you’ll have to get the phone completely replaced.
Update: according to Ars Technica, this happens because January 1st, 1970 is the first day of the Unix epoch, and that allowing the phone’s battery to go completely dead (or disconnecting the battery) will reset the date.
I agree kristinwest91 letting the battery drain seems to be working. Looks like Apple is rolling out an update that'll keep this from happening going forward. If you changed the date to May 1970 or earlier and can’t restart your iPhone, iPad, or iPod touch - Apple Support