It makes absolutely no sense for anyone to play around with the date of their mobile device as it is known to cause issues with push services and mobile network. However, if you are feeling adventurous and decided to go back to the 70s and set the date of your iPhone to 1970, then you will brick it. The only way out of the problem is to then take your iPhone to the Apple Service Station and get a replacement. After an extensive media coverage, Apple admitted to the bug and promised a fix.
The fix, it seems has been rolled out in the form of iOS 9.3 update, which is in Beta with the developers. Those who have tried out the update tell that the bug has been fixed by Apple and you will not have any more bricked iPhones because of an incorrect date. The news was confirmed by users on MacRumors Forum who state that Apple will now, not allow you to input a date that is older than January 1, 2001.
In case, you still manage to brick the phone, you simply will now need to connect it to iTunes and restore to the factory firmware. No more the need to run to the Apple Support or sweating about your plans of walking back into the past.