They give you three minutes to read the prompt on screen and seven minutes to answer the question. When you complete the question the interviewer will ask you if that completes your response, and if there is time left then they will chit chat with you, which will not affect your interview.
They are looking for you to answer with conviction. Don't second guess yourself or say you "might do this" or "would probably do that."
Know your shortcomings, and be able to address those. They want to know that youre a good candidate that isn't perfect, but can fail and adjust. From most MMI practice questions that is one of the major overarching themes.