The free foot moves before the weight change
When walking backward, the foot that is to step back next may initially still be in front of your body. Once it no longer carries weight, it is the free foot. If it stays in front for too long, it has to travel a long way in little time just before landing. This is the delayed start you practise, not a new step sequence.
Moving the free foot back earlier does not mean stepping onto it earlier. Its path and the subsequent weight change are two distinct actions. The foot passes close to your body by the standing foot, then moves in the familiar backward direction. You are not looking for a pause beside the standing foot, and you do not take an extra step there. As long as the front foot is still carrying weight, you do not pull it away.
So the exercise begins at a suitable point in the sequence you have learned, not necessarily with your feet together. Keep your arms still at first: practising arms and legs separately keeps the task manageable. If the movement only feels constrained when dancing with a partner, that is a different issue from this solo foot path. For a turn that stalls when dancing with a partner, you can find tips under blocked turning paths in Viennese Waltz. Here, your only point of focus is the start of the free foot's movement.


