Ok. I got it to work by using tasker variables. I set a variable %Pomodorostart to %TIMES when a pomodoro starts. When a pomodoro finishes I set another variable %Pomodoroduration to %TIMES - %Pomodorostart. I then only submit a value of 1 to my pomodoro beeminder goal if %Pomodoroduration is greater than 24 * 60, i.e., a little less than 25 minutes, but measured in seconds.