I hate both current implementation (a pain to add marker pair), and this topic’s idea (additional keypress to add a single marker).
Ideas of the people above me are quite nice, but I have mine: click on the time bar to add a single marker, as it is now, but click and drag to add marker pair (add one in the place of mouse down, and the second in the place of mouse up). Also auto-scroll when the mouse cursor is at the right or left edge.
And also display frequency for time differential measurements (perhaps also for automatic measurements on the waveform).