There are a number of options for front desks (whether it be an office, hotel, museum, shop or otherwise):

1. Single worker on a 10-4 Mon-Fri schedule (reduced hours across all days) and the front desk is unstaffed at lunch and during bathroom breaks. Customers have to attend during reduced hours.

2. Two or more workers with overlapping hours most of the week, but occasionally they are by themselves. There is always at least one worker at the front desk (whilst others are taking lunch or not working that day).

3. On one day of the week, another person sits at the front desk (and performs another role the other 3 days of the week they're working).

4. The business no longer has a staffed front desk. If someone is visiting you in an office, you collect them from the lobby/waiting area.

Sure it does. Any customers who call on Friday will quickly learn you are closed, in future they'll call mon-thurs instead. The no-productivity-hit claim is based on the fact that both businesses and customers are adaptable and quickly change their behavior to match new norms.

Most likely the widget is being ordered online, and, since everyone knows the factory is closed on Friday, it'll be made and shipped on Monday, and delivered on Tuesday/ Wednesday, regardless of whether it was ordered Thursday or Friday.

If the factory has encountered a backlog, the mechanism for worker overtime or a 2nd shift still exists.

You can rotate for the week-end shift too.

Once the companies get larger, you just strategically set-up the work schedules such that people only show up four days a week but all shifts are covered.

Even if the rules don't apply to them, that means that as an employee, I can choose a small company and have to work five days, or choose a large company and have to work only four days for the same pay. This will make it even tougher for small businesses to hire workers.