This is a much better way to do it imo. The 5 minutes at the end is usually just a courtesy, and the interviewer isn't expecting to get grilled.

Some (not all) hiring managers even treat this as an additional way to assess you, to see if you're the type of person who has done their research on the company and asks intelligent questions.

Much better to set expectations upfront and ask for half hour chat with the hiring manager (or even other team members such a tech leads) separate to the interview.