I've done the four ten hour day thing. By the end of the third day productivity begins to drop off. Plus if you have half of your people working Monday thru Thursday and the rest Tuesday thru Friday invariably you wind up with an unofficial company motto as things fail to get mentioned
https://www.youtube.com/watch?v=V2f-MZ2HRHQ
https://www.youtube.com/watch?v=V2f-MZ2HRHQ