Google had started releasing stock Android apps in the Play Store that allows the company to update them individually. It has already released the Google Camera, and a dedicated app for the messages. Now, Google has released the stock Android app on the Google Play Store so that everyone can use it even though their phone comes with a custom clock app.
If you don’t like the Clock app from your smartphone manufacturer, you can stop using that, and use the Google Clock app instead. It has a Material Design UI, and even supports Android Wear. It integrates clock, alarm, stopwatch, and timer functionality into one single app.