Time really is a mystery

So, I find it very weird that my clocks change themselves. I have the time on my cable box and also on my alarm clock next to my bed. They are maybe six feet apart max. Well, somehow I keep noticing that my alarm clock falls behind my cable box. Right now the cable box says 11:15 and the alarm clock 11:12. I just matched them up about a week ago because they were five minutes off and in a weeks time either my cable box gained three minutes or my alarm clock lost three. I don't quite know if someone is playing a sick trick and sneaking into my house and changing them or if somehow seconds really slipping away, I guess it will remain a mystery.