Task Estimated Time (EST) Countdown Timer
If you give your task an EST (as explained in the Task EST section), your countdown will be based on the EST you set.
For example: If you estimate that you will complete the task in 15 minutes, and enter 00:15, then the live timer for that task will countdown from 15 minutes till it hits zero.
Pomodoro Countdown Timer
Pomodoro is productivity technique that many people use whereby you alternate between a fixed focus work session and a fixed short break time. You can set this on from preferences available both via the Home screen profile dropdown menu as well as the Focus Panel Quick Preferences (see here).
With Pomodoro switched on, the timer will count down from the work time you set and automatically switch, with a notification sound, to the set break time once the work session is over.
Time Tracking Timer
If you you don't have an EST set on a Task, nor do you have Pomodoro switched on, then your timer will count upwards and act as a basic time tracker.