Lois, it all depends on how clearly you can write to explain time-shifts. It's a difficult thing to do. You could establish fixed references....erm..e.g. an autumnal oak-tree seen through a window in one time period, and refer to it every time you were in that time shift. It would have to be more complex than that I'm afraid. How long have you got to do this? Good luck if you go ahead. You refer to 'teacher', if it's a piece of course-work you will have to sacrifice other ideas I think.