Like all hunting skills, some folks have a natural knack for knowing when to draw. It is difficult to teach because every scenario is unique.
In heavy cover, which most of my hunting is done in, it doesn’t really matter, other than erring on the side of drawing early so as not to miss a small window to shoot.
If I’m hunting open terrain and/or after leaves have fallen, I’ll wait till the deer is looking away or vision obstructed by a tree.
If it’s inside of 20 yards, it doesn’t really matter if it sees me draw and freezes, it’s dead.
To your specific question, one of the big benefits of the saddle to me is tree between me and deer. If I can use that to draw out of sight(or less in sight), then rotate 10-30* around tree and make the shot, that’s ideal. Tough sometimes though, if you can’t see the deers eyes but it can see your bow. Want to avoid that.