You don't understand relativity. Time isn't changeable, it's simply relative to each individual. It says nothing about time being changeable or having a beginning or anything like that. Don't tackle subjects you know nothing about purely for the purpose of name-dropping a prominent scientist in order to add weight to what you are saying.
I can't speak for all atheists, but i personally am not guilty of knowing 'nothing about nothing'... i simply do not know everything about everything, & i reserve judgement on things until empirical evidence is presented. I am not adeist, as i do not know that the universe was not created, my personal opinion is that it probably was not, but i am happy to achnowledge that i could be proven wrong on that.
I am however atheist (& when it comes to the god of the bible, i am most definately an anti-theist, & i'm sure you needn't spend too much time guessing why), as the idea of a personal god (with whom one can have initimate fellowship) is demonstrably subjective to the point where to take someone elses testimony on it seriously would be favouritism in the extreme. Christians can believe what they want, but they deserve to be taken no more seriously than those who continue to spot Elvis every year. Because we know so much (no, not everything, but a hell of a lot) about the history of the Ambrahamic religions now, it is somewhat absurd to believe that any of the god's they worship are anything more than man-made. If the universe was created, then these god's had nothing to do with it. At least, they had about as much to do with it as the tooth fairy did with the invention of dental braces.