This is an aesthetic or control joint, not an expansion joint. These joints are used to control cracking. They are usually required every 144 sq. ft. of area. Refer to the particular manufacturers installation instructions for specifics. Also, I do not think this is a three coat system. Most likely it is a "one coat" - base coat plus finish coat. There should be a 1/2" - 5/8" gap at the window with backer rod and DOW 795 caulk installed.