I have similar thing with my business. Usually Monday and Tuesday are very busy, than it gets quiet. I guess many people surf the web during weekend, than they call on Monday or Tuesday when our office is open and make purchases. People don't want to buy during weekend, because they know it won't be processed untill Monday. I guess Thursday and Friday they are thinking about weekend and they know that orders placed by the end of the week will most likely arrive next week. So there is no point to shop online by the end of the week. At least this is what I think. I guess it depends also on type of your business and products you sell. Also sometimes you have one very busy week and than next one is dead. I used to think it was something with ads, but it is not. It's just the way it works. No consistency on weekly basis. As long as monthly sales are consistant I don't have reason to be worried.