I don't do anything until around May myself. A lot of the time my areas are to wet to disk earlier anyhow. Also this year I left several acres of standing corn. I don't want to disk that under while the deer are still eating it so this year will wait until last minute to bush hog it and disk.
A lot of it depends on what you are starting with and what you want to plant too. If you are starting a plot in an area with a lot of wild stuff already growing, it's a good idea to bush hog it as early as possible so it can rot down some before plowing or disking later on.