"To be in time you must be on the beat."
Mabye in the body, but certainly not in the feet! see:
https://www.ballroomdancers.com/Message_Board/view_messages.asp?MsgID=23818&PageNum=1
Doug and Clive are obviously on the right track. To a first order approximation, the time of the SQQ steps is indeed very close to three equal parts as they have observed. Later on, with more control, the step associated with the last quick will end up being drawn out to take the longest amount of time (and the first quick's step will be shortest, only about a beat long). But for starters, aiming to divide the time evenly, 1.3 beats each, isn't too bad.
At the very least, it accomplishes the first lesson of foxtrot timing: the steps are planted to support a well timed body movement, not to tap out a rhythm. Footwork only becomes rhythmical in certain syncopations, never in basic SQQ actions.