I did these 24 blocks while watching the college football game Sat night. I did them assembly line, but thought it worked out to pretty much "10 minutes" per block. Backing is fleece. I used a bag of 4 1/2 inch fabric squares I had on hands. Think the main thing on this block is that the 5 squares be the same size. However, if you wanted the inside block to be bigger in relation to the outside block, there is no reason you could not make that square larger.