One other problem is that the whole 40 hour thing is also a farce in the presence of salaried positions - most places want you on site all day, under the assumption that they can keep you during crunch. If you are only working 4 days, unless you have infamous "come in on Sunday" talks with your boss, they have less opportunities to keep you for free overtime since you are salaried and they often put on weekly caps on extra hours before they have to pay overtime (or none at all, depends on the company).