In my experience, the length of a program and the skill set and/or minimum acceptable teaching experience in teaching area for new instructors dictate the periods of orientation. For example, for a 6-9 month certificate program, the orientation can be as short as two weeks for new instructors with 3> years of current or recent experience teaching the subject. For those without experience, minimum of 4-6 weeks (usually a course/module) should be sufficient.