Here's my summary about the whole CMOS time bomb issue:
First of all there are two sets of clock in PS4 system, one is RTC clock (also called kernel clock), the other one is system clock (shows on upper right corner on main menu). System clock is just an offset from the RTC clock, and the value you set in settings doesn't reflect on RTC clock but rather changes the offset of system clock from RTC clock.
So when PS4's RTC battery dies, RTC clock will be reset to 1970, and will cause 30391 error when you try to launch any game (PSN, retail disc and fpkg). Someone on twitter said 30391 error is caused by the trophy data installation process, which checks RTC time.
Now to fix this error, you need to replace the battery and sync time with PSN server (which requires you to sign into your PSN account on PS4), so you need to be on latest firmware. If you are on 5.05, you can use react ps plus payload to manually set RTC time (not sure if 5.05 even throws 30391 error at you). If you are on 6.72-7.55, there's no fix yet, but the error could be bypassed with goldhen or mira+todex (they have debug trophy feature which somehow bypasses the date check).
That's pretty much everything about CMOS time bomb. Correct me if I made any mistake. BTW I'd recommend changing CMOS battery on 6.72-7.55 systems every 5 years before they die (I made a post about it but it's really simple, just leave PSU plugged in when you change the battery).
