I was at a conference last week and learned about a terrific timer for my iPhone called Performance Timer. It counts down your specified time, and then changes from green to red as you go over.
What makes it superior to the default iPhone timer is its large font, there is no alarm when time is up, and your screen never goes blank, so you can read it for your entire talk. Really easy interface for the stressful time that you are setting it up. Or, if you are the timekeeper for someone else, they will be able to read it from 20 feet.
It is free in the Apple App store. I looked but did not find the Android version.
Here is a review from the web.
Rating: 5 – 9 reviews – Free – iOS – Utilities/Tools
Performance Timer is a large-display countdown timer developed to be used to monitor the time remaining in a performance, presentation, etc. Performance Timer does not sound an alarm when the time runs out. Rather, when the timer reaches zero, the numbers turn red and the timer starts counting up so that you can see how long you’ve gone over your target time. The time can be set from 1 to 99 minutes.