i've facing this problem since ios 8 update (i am on 8.4), but somehow this past month the clock starting to moving ( i didn't know what caused this ), but maybe it will helps, here's the chronology :
my phone keeps disconnecting from my wifi, and will auto reconnect. the phone wouldn't connect to an android hotspot after disconnecting saying the password is wrong or something (cant remember lol).
the bluetooth is dead?(spinning wheel of death)
the clock stop moving when device is locked for > 2 minute (stopwatch and timer is also stopping when device is locked). this happened when the device is not connected to power source.
i have followed this post http://blog.gingerlime.com/2010/iphone-running-late/ , but i modified the plist file to update every 6 seconds. and it doesn't work as it should, so as a frustation (though i didn't delete the plist). i used activator to run the sh script everytime i wake the phone. after using this method since november 2015, now in the past month the clock started to moving even when the device is locked. but after the phone is dead or restarting the clock changed to maybe random clock and sometimes different day lol. so i didn't know what caused my clock to start moving. as for the wifi or bt i still have the same problem.