focus timer. calendle has also a build in focus timer which allows you to focus for 52 minutes. Why 52? 25 minutes was too short. 52 is 25 reversed. And the cross sum of of 52 is 7.

You can control the timer via the F button in the app or you can use text commands. Just write into an empty bullet text and press enter:

calendle also keeps track of you focus sessions (◆). To remove them you can use the button or the command "timer clear".