I like to draw when an animal cant see me. This doesnt always occur, but its my preference.
So I practice holding as long as I can offseason and at the target butt, often not even releasing an arrow.I like to do this at a different time than actual shooting. Its my strength/form builder, not my shooting practice. Just in case the deer stops or is slow showing itself, which happens often. The deer are skittish around here and will pick you off drawing a bow very easily.
During hunting, I have no idea how long, as said here already as long as it takes. Sometimes a second or two, sometimes seems like an eternity.
But I at least have the ability to hold if I need to. Your strength will increase very quickly when you practice holding, not worrying about the shot itself.
When you start to shake, you have held too long to shoot accurately. Which is okay while practicing, but if you are drawn on an animal, you want to reconsider releasing an arrow at it at this point.