The length of outages will vary from place to place because the means of triggering the blackouts will cause varying levels of perturbation of the existing infrastructure. Some areas will be able to recover more quickly than others. So it is difficult to give great assurances here other than to say the target is to have at least several days of power outage to make the experience grueling and even reach life-threatening conditions. Keep in mind that the goal is not to carry out in the annihilation but simply create fear in the hearts of the populace, for them to look for a savior, and the resulting pressure on governments will be intense to find an answer and prevent a repeat of what has happened. So to have such a terrifying and painful experience will be a great motivator to accept the extraterrestrial Disclosure offer of assistance and that is the purpose of the exercise, to soften you up so that in your desperation you will leap at the chance to get some help from a perceived higher power.