how long the tour of duty for a SACEUR is?
There is no specified tour of duty for a SACEUR, although in recent years the length of service as SACEUR has generally been around three years.
During the Cold War SACEURs tended to stay in post for longer periods, often for five or six years, with the record being SACEUR Bernard W. Rogers' eight years in post from 29 June 1979 until 26 June 1987.
The shortest terms of office for SACEURs have been slightly over one year. Such short tours of duty have been the result of a SACEUR taking another position, such as Chief of Staff of the Army in the case of General Matthew B. Ridgway or Chairman of the Joint Chiefs of Staff for General John Shalikashvili.
And of course the first SACEUR, General Dwight D. Eisenhower, left SHAPE after somewhat more than one year because he was resigning from the army to begin his candidacy for President of the United States.