I find that I enjoy mowing and most of my outdoor chores and projects for a certain amount of time. Then I get tired, stiff, or just sick of doing that particular task.
Unless the entire place somehow *needs* to be bush hogged today, I prefer to mow for as long as I'm enjoying it, and then finish it up another day. I don't have a commercial farm that is making me money, so I ought to enjoy the process.