After opening the webapp the first time (I can restart this by refreshing the browser, but the data shouldn't have been edited yet), the I see this:

Then, if I go to the next week and return to this week, it's ok. Then Saturday appears.

Saturday is an important day: it's the first day of the weekend, praised by so many people. It's only secondary to Friday. If might be able to get away with lacking Monday, but we can't lack Saturday!