Set timer with alarm for 20 min. Start the online timer set for 20 minutes. Sound alarm notification is optional.
How to use 20 minutes timer
The timer will tell you when your 20 minutes has run out. It will keep counting upwards when time has run out.
Sound notification (alarm) is optional. You can keep the timer running in the background if you for example open a new tab. If you have sound notification the timer will tell you when time is up.