Thanks for suggestions!
Solution are GPS( too fancy), RTC ( less fancy, need backup), crystal (unknown territory for me), I even look at 555 but I doubt its accuracy since it's based of capacitor.
Can someone explain why it's always about 700ms shorter then desired? If my problem is a hardware inaccuracy then why it's not something like +/-700 but always less? Maybe internal clock is running little bit faster? I am curious at this point.