Set the way the pulse width is changed by click & drag.
IF THIS OPTION IS ENABLED:
Click on the desire time slot marker or right-click on the pulse (anywhere in the pulse area) and drag its right boundary. You will move the boundary between this slot and its right neighbor. The rest of the waveform will not be affected as the sum of widths of these two pulses is kept constant.
IF THIS OPTION IS DISABLED:
Use shift–click