I think one flaw is that everything happens over the weekend meaning the developer has Friday to understand everything and then be ready for Monday. Personally, I don't know half the issues I might run into when I first start a new project, and if they expect me to just "make assumptions" the solution I end up with could be miles from what the wish for (both in direction and size). If it was Monday to Friday (or Monday to Monday), there's a chance for me to ask questions, get smarter and iterate on the solution - same as I would if I was actually working.