DE Timer од Erin Meow and Dhiviya Rajan

Here you will have a 2-in-1, stopwatch and countdown timer for managing your time and schedules. You may use the stopwatch with as many "laps" as necessary or the countdown timer with pause, resume and presets support. When the timer finishes countdown, the extension shows a desktop notification with a high priority where it plays a timer tone to alert the user.