Complex sentence: Pedestrian signal heads at either end of the crosswalk display the upraised hand (don't walk) signal until the HAWK beacon displays the steady red signal, at which time, the pedestrian heads display the walking-person (walk) indication.
Split into simpler sentences: Pedestrian signal heads at either end of the crosswalk display the upraised hand (don't walk) signal until the HAWK beacon displays the steady red signal. At this time, the pedestrian heads display the walking-person (walk) indication.