I didn't see directions as to when to attach the pocket. I had the bag assembled for the most part before I saw the picket sitting there, detached! I was able to attach it before whip stitching the lining closed, but I had to be careful about not catching in part of the bag. After you quilt the outside pieces, I would place and stitch it then.
Here's my first attempt without the side ties. I may still add them, depending on what I choose to do with the bag.