I'm looking for something to display a timer/progress animation.

I am a high school teacher and one of our Covid-19 safety steps is breaking the semester up into quadmesters. So instead of 4 75 minute classes, each student will have 2 150 minute classes which reduces rotations and creates a bubble of sorts. Anyway 2.5 hours is crazy long so I want to show my students our progress. A low tech option is a slideshow that I can manually change to match time/progress...say every 10 minutes, with more significant markers at quarter and half way, but is there a more elegant tool?