Unfortunately, time is what matters. If the person is not receiving adequate oxygen then permanent brain damage occurs and only takes approximately 4 minutes for brain damage to occur and death can occur in 6 minutes.
While emergency situations will arise and often when we least expect; take the time today to invest in a 3-4 hour face-to-face class to learn the basics of CPR and how to effectively operate the AED. Remember, it all starts with "Call 911, Grab the AED". Unfortunately, the problems lies in that many American people don't know where or what the AED is.