I don't remember if they had a designated amount of time set aside for you to think about an answer during my MMI last year but I do know that in an MMI the interviewer wants to hear your thought process so I basically spoke as thoughts came to mind and said things such as "I recognize this is a really challenging situation- if this was the case then I think it's appropriate to do XYZ, but it's also important to take into consideration family wishes etc. but at the end of the day my job as a physician is to educate and care for my pt so this is what I would do short term w/ long term goals being XYZ".