There are few applications which you can use on Windows laptop.
1. SnapTimer : This application can popup timer and show you the time to take the break. It's free and also very easy to use. In fact you can easily learn it without any helpfile.
2. Cooktimer: Same as snaptimer but adds few extra options which you can explore if need be. It's also free and easy to learn to use.
As for Redmi phones timer, here's how you can use.
1. Open Clock application from tools folder.
2. Tap on timer tab at the top.
3. Look at the timer options at the bottom.
4. Check for add timer option.
5. Select 30 minutes option.
6. And set it the moment you start working.
You have to reset the next time you start working again on laptop. Hope this helps. And take care of your health.