Several users have reported that if you change the date of your iPhone, iPad or iPod touch to January 1, 1970, your device will be permanently bricked. This bug affects any iOS devices running iOS 8 and 9, and with a 64-bit processor. 64-bit processor iDevices include iPhone 5s and above, iPod touch 6th generation and above, iPad Air and above, iPad mini 2 and above, and iPad Pro. You have to bring the device to Apple Store once bricked as not even restoring from iTunes is going to work.
Updated: Apple has confirmed this bug with a support document. An upcoming iOS software update will fix this issue.