Obviously a lot depends on your conditioning, your age, etc. However I think I would have some concerns with the concept of "riding in a week what you want to ride in a day".

While weekly mileage is important so is maximum time and mileage at one sitting....ie; your butt. If you rode 20 miles a day, seven days a week most people would not even be close to being able to complete a century. It is imperative that you get your butt, hands and core to the point where a 60-75 mile ride is doable.