I can take some time to get to the answer but it is still going to be six. And, each circumstance is different, but I would still struggle to get to five or seven as the answer.
First, why six? To capture any kind of coffee, breakfast or lunch business, you have to be open on every business day. You can't close on Mondays if you really want to capture the business market. Saturday is the busiest day of the week in most retail circumstances so you definitely want to be open then. Open Monday –Friday plus Saturday equals six.