Using above filters you can filter the subtasks based on label or based on assignee – choosing one assignee unmarks the rest and shows all subtasks assigned to this assignee. Click on it again and you will see the rest.
To track the time of each subtask, click on the button or drag and drop the subtask in done and set the spent time in the popup. The remaining time can be calculated either automatically or manually. Note! Tracked time is being saved automatically in the timesheet.