Everyone here has some great ideas, and to try to prevent rushing or skipping, I think I want to combine a few suggestions.
I think we'll have a paper in the back on something the speaker can see. Each presentation can be broken into 10 minute chunks then. Green for the first 1/3, Yellow for 2nd, red for 3rd.. Then at 4 minutes remaining, go to fingers up, then a black paper if over time. Easy enough to use a 3 ring binder with the colors in it and just flip as needed. Thank for everyone's ideas!