This is the kind of question I would have to talk to someone about over the phone or on skype- especially explaining essay structure.
To tackle the question, you'd have to present your ideas briefly in the introduction, quickly stating your final conclusion without going into detail.
From there, paragraph to paragraph, you have to tackle the various examples of time represented within the Maesta- thematically. It is always good to have a paragraph at the end on an unusual perspective, flipping the question around- for this example, on how perhaps Duccio wasnt representing time but rather something else.
Am very happy to discuss this properly in the interview.