Is it OK to ask for 1 minute to gather my thoughts before concluding?
Yes, absolutely this is okay.
Keep in mind that in an interview situation, a 1 minute pause feels like 10 minutes to the interviewee (you in this case)?
Just realize to the interviewer, it's not a big deal. We just mentally start thinking about emails to reply to, our calendar, what's for lunch, etc...
So better to pause briefly and end with a strong concise, conclusion than to rush it.