window of opportunity

The EMTs had given Lolly magnesium on the ride in, Dr. Salazar said, and that had put the injury in "slo-mo." And with stroke victims, "time was brain," she said; the quicker there was treatment, the better the odds of avoiding permanent damage. "When she got here, we gave her a clot-buster called tPA. Great drug if the patient gets it in time―acts like Drano on clogged arteries―but the operative word here is if. Time-wise, there's only a small window of opportunity. When the blood supply's cut off, brain cells begin to die. I think you'd better prepare yourself for the fact that your aunt will most likely have an altered life." "Altered how?" "Too soon to tell. We'll know more in the next forty-eight to seventy-two hours."