Except that other people have also received this notification and we weren't all coincidentally messing with the date.
It does seem to be tied to 9/6/2015 though, as I just received it the first time I unlocked my iPod after midnight today.
VSMac had set the date to after midnight on 9/6, which is when the pop up is triggered. Every other person here including myself received this message shortly after midnight on 9/6. Hence the pop up being preprogrammed for the date. If your phone was on and being used, the minute you went to the home screen after midnight or closed an app, you received the pop up. If you didn't go to the home screen or just locked your phone after midnight and went to sleep, you may not have seen the pop up until you unlocked your device, like you mentioned, after midnight on this date. Everybody is receiving the message at different times because it is only displaying on the home screen while in use. So when midnight hit, and your device is either locked or you have an app open, you won't see the message until whenever you go back to home, after midnight. Or in the morning, I presume many more people will be seeing when they unlock iPads, etc for the first time. VSMac had found this hours before anyone else, while messing with date and time settings. Then midnight hits, and boom...