Enter duration in source panel to get out point.
Enter an In or Outpoint in the source panel. Then drag along the source panel timeline and see a duration in real time. Also, enter an In or Outpoint in the source panel. Then enter a Duration to get the three-point edit.
Jim Simon commented
You can get a duration by pressing + before the time.
For example, +2.0 will move the playhead two seconds in from the current In point to mark the Out point for a two second clip.
Stewart Shevin commented
Editors work by marking not only in and outpoints, but often by entering durations.