Controlling settings, permissions, and membership within Teams and channels
Hello Donnie,
My name is Juan Pedro, I am an Independent Advisor and consumer of Microsoft products. I will be more than happy to assist you today!
I am sorry to be the person bringing the bad news, unfortunately, this is not an option.
However, you could download a timer to your device and share your screen for your students to see the timer.
I hope this helped. I will be around in case you need something else.
Thank you.
Screen sharing to display timer on a device would be impractical since screen is usually shared for individual aplications presented and/or by multiple presenters eg. business environment.
Also salute the idea of including timer/clock option that stays visible to all participants throughout meeting.
Thank you for considering Donnies initial suggestion and if could be passed on MS Teams dev team.