Also...There really isn't a "cookie-cut" answer that will apply for all the different product types/categories. It also has to do with the popularity of your item and the season.
The best way is to research your own market by doing a completed item search to see what is working best for other sellers and to also experiment with your own results.
You should try other days and not just limit yourself to Th-Sat. From what you are saying...your own experience should tell you Saturdays might not be working for you and you should experiment with the rest of the week.
Good Luck!