Within Teamwork Projects, you can add tasks from your projects as new timers in the desktop Teamwork Timer app.

To add a new timer, click on the '+' to the bottom left of the timer window as below:

When you choose the add timer option,  you will then be able to create a new timer by adding a name or select an existing task from your Projects site to log time to:

When selecting an existing task for the timer, you will see the option to select the Project and a task list within it:

In the 'Select Task' modal, you can also create new project tasks directly in the timer app:

You can also drag and drop tasks from your project in Teamwork Projects directly into the desktop app to create new timers: