Software for keeping track of time in a presentation

Once I attended a lecture (a powerpoint presentation in Windows), where a small digital clock showed the remaining time in the corner of the screen (even when the powerpoint presentation was in full screen). Before beginning the lecture, the person set the clock for one hour, and perfectly finished the lecture just in time.

Is any similar software available in the Manjaro/Arch repositories, which would allow the person giving the lecture to keep track of the remaining time during an online lecture? I plan to use Libreoffice impress/PDF document in presentation mode.

The system clock in the panel cannot be seen when the presentation is in full screen mode.