I dont want to just dive into a question about a personal experience story, I would want to first structure my experience specifically for that question, is this allowed?
During McK PEI, is it ok to stop pause and structure response for 60 seconds before answering?
As opposed to the case interview, pausing for 60 seconds is not recommended for the PEI. Just given the overall PEI time of roughly 12-15 minutes, 60 seconds is already a big portion of time which does not add any direct value and will get your interviewer somewhat bored watching you sitting in silence.
At the same time, the direction of the questions is clear by the 3 dimensions and McKinsey expects you to have "enough" examples from your experience to explain and demonstrate for the PEI, so for this a relatively quick answer is expected. Of course, pausing for a couple of seconds to think about the question is perfectly ok and makes your interview example also feel less rehearsed.
Concerning structuring your experience specifically for that question, it's mostly the case that you don't need to rethink your whole example, but will mostly need to tailor only the "P" (Problem) of the "PARADE" framework to the specific question of the interviewer. And this should also take siginifcantly less time than 60 seconds. (for more information concerning the PARADE framework and structuring your PEI, I also wrote a blog post about that on http://mckinsey-pei-blog.consulting-case-interviews.com/how-to-perfectly-structure-your-mckinsey-pei-example/)
I agree with Robert, taking such a long time before any fit questions is not recommended. That’s because there will be expectations that you have prepared for the questions in advance. Having said that, it is definitely better to take some time rather than give an immediate weak answer, although you may not get full score if you wait for 60 seconds.