Way too many variables. An elk can come up on you pretty quick and give you an opportunity to draw and keep coming for a very quick shot. Other times you see them hang up after you have drawn and they can stand there for a long time. I would try to shoot for a minute if you can. You may have to hold it longer than that or just let down and try getting on another elk if you can't hold it or are shaking too bad to make a good shot.