Your idea sounds great!
At present, you could only lock the meeting manually when you are in Teams meeting. There is no such time settings could control when the meeting is locked.
I have created a feedback in Teams UserVoice and you could also vote for it here. Microsoft will always focus on customer’s feedback and experience. Some new features would be added to the services based on customers' feedback in the future, and your good ideas will be very helpful for them to improve the service.
Your time, understanding and cooperation will be highly appreciated.
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