If you set your time to January 1st 1970 OR January 19th 2038 it will brick depending on your iPhone.
January 1st 1970 is the Beginning of Unix time and will brick iPhones Above 5S.
January 38th 2038 Is the end of Unix time and will brick any iPhone Below iPhone 5s.
Why is a second date Added and its not part of the 1970 rumor?
It is because at January all 32bit with the Unix Epoch Time Binary will exceed the number the system can count and will reset to January 1st 1970, Where the binary was first completed and used.

Explaination of Unix Epoch (noob friendly)
Unix Epoch was First coded and made with this Idea in mind, "Why use the blank/blank/blank to count time on unix based devices?" So what they did was make a clock that used a format of counting seconds instead of second then minutes then hours and so on, But this eventually escalated massively and expanded than the purpose of counting seconds, so what we use, Androids, Windows, Apple, anything that consist of modern technology that is commonly used by many people over the globe, has this very "completed" system so they say, but you know how it goes, everything will eventually come to a end.