Q. Once started, how long must I continue the plan? 

A. SEPP distributions must continue for the longer of: five years from the date of the first distribution or until age 59-1/2. If you begin distributions at age 54 1/2 or later, you need to continue for 5 years. If you begin distributions before age 54 1/2, you need to continue them until you are 59 1/2.
Once you’ve met the five-year or age 59-1/2 point, this is called your first modification date. At this time you can modify the distribution amount – you can withdraw more, or less, or even stop distributions altogether (until you reach 70 1/2 when the Minimum Distribution Rules apply).