I would say any week day would be good, as many people have work or school. I think the ideal day and time would be probably be Monday morning. Most people dread Monday and don't want to do anything that they don't have to do. The earlier you go the better chance you have of most people being busy with other obligations. I've shopped at all different times of the week, and I do honestly feel like the times where I deal with fewer crowds, and am early able to find everything on my list, is definitely weekday mornings!