Sometimes a whole draft. Well, it depends. I might see that the punctuation isn't right, or the line break isn't quite right, or I may want to add or subtract something. If you copy something out by hand, before you move onto the typewriter, you've already gone on making minor changes. This is an intuitive part of the creative process, and one that's eliminated by the use of word processors.
People get such a completed-looking copy that they think the poem is done.
The word processor doesn't take as much time as actually forming the letters with your hand at the end of your arm which is attached to your body. It's a different kind of thing. They don't realize that this laborious process is part of the creative process. I've been writing poetry for many, many decades. Then you do that.