Why was my iphone lock screen time wrong?

So I grabbed my iphone which was sitting on the table, I pressed the bottom button to bing the screen up and the time said 5:47 and then I locked the phone and brought the lock screen back up again a few seconds later and it sai 5:49 I'm very confused why would this happen?

I think it is something to do with the GPS in the phone or a bug in the new Firmware, I have seen this problem before on answers. Honestly I would go to the apple support website and post something there. Apple customer service has been pretty helpful for me in the past so I would give it a try, here is a link

http://www.apple.com/...e/contact/

hope this helps