Earlier quoted context omitted.
Seems questionable to use the local time for that. System time isn't exactly a trusted quantity, is it?
iOS does it that way. My iPod touch always forgets date and time when it runs out of battery. After restart you can't do anything in the App Store or on https websites before you've set the correct date (it defaults to 1970 which is when the iPod was first introduced I believe).
IE, Unix time started then.