I know it sounds crazy but it has happened quite a few times to me already. I wake up at about 8am realising my alarm clock did not go off. It turns out that my phone clock is reading 6:24am! What is weird is that the lockscreen time is correct but the phone clock is wrong. I tried to look up google to see who else has this problem and I can't really seem too many reports of this. Leave a comment if you found this happens to your Galaxy Nexus as well. If you have a solution, I'm all ears.