(I'm totally making this up but I deal with software distribution for work which has a client/server setup likely similar to stores like PSN)
Sony flips the switch at 12, but your console which is the "client" doesn't see that until it receives word from the store. Even though you all SEE the same store - which is to say, it appears the same - you may be hitting various distribution points/servers for the store information. These servers ALSO have to sync up with the primary site that Sony updates at 12, which is why different people see it go live at different times.
The web store does not have this problem as it can access the central store more directly and force the download to your system - so that can be quicker.
Idk but it sounds like it could be right