Just before the finish! First top and bottom, then side and side.I'd have to go back and check the directions, but I think Bonnie had us put on each border as it came, so first the narrow Neutral, then the 4-patches, then the alternating squares. There are some good reasons for doing so, less thought required putting together the 4-patches and checkerboards than the way I did it. I am still just amazed at all the ways things can get twisted together and done wrong when you are just using two colors! The same way I feel I get better results by putting the sashing on around the blocks (so I don't have a big piece and a narrow piece), I just don't like going around and around like that and finds it gives a chance for ripples, loose seams, stretching or other issues.
First, I did stay stitch all the edges on the "bed" of the quilt before I attached the narrow binding on the long sides. Then I put on the long sides, with my extra row, the 2 WoF neutrals was just long enough.
Then, as I constructed the borders I put together the alternating red/neutral squares with the 4-patches. When I got up around 8-units long, I stay stitched both sides (4-patches and checkerboards). The top and bottom borders are made as a unit of the narrow, 4-patch, checkerboard. The long sides already have the narrow on the quilt and are the long sides plus corner units. With the outer stay stitching already done, these border seams will be the last of this project!!
And you will notice (maybe) in my picture that I am using my color coded clips to tell me which end belongs to which side
is really an easy-to-do improvement in keeping me the right directions.