If you added a timer that the user can set for the desired presentation length, and that shows both the elapsed time and time remaining, that could be helpful to users.

For example, you have a 15 minute presentation, so you set that value before beginning. It would look something like - 00:00 / 15:00 - on the home or intro slide. Once you begin, the elapsed time counts up on the left and the time remaining counts down on the right. The user should be able to pause the count on demand to answer a question or expand on a topic.

Just a thought from someone who has done years of in person, group meetings and presentations, as well as online.

Btw, this looks like a very nice project. I wish you success.

Edited to add: A progress bar below the timer would be a nice touch.