Add option to display 'Closed all week'

I guess this is a valid feature request, given you have selected to show all days, even if they are closed.
However, for most entities, leaving all fields empty, just means that the entity has unknown, or no opening hours.
We'd need an extra option, I suppose, to distinguish etween the two.

For starters, you should change function office_hours_field_formatter_view(), and remove the first lines:

  if (!$items) {
    return $element;
  }

If you have something ready, please post your results!

For a definitive solution, we need a solution like here: #2044465: Add links 'clear' and 'apply to all' to Widget to improve usability

Let's refocus this issue to adding a checkbox. See attached image.
Still need to figure out the exact usage. (what if: hours are filled and checkbox is set? Hours are empty and checkbox not set?)

Agreed with checkbox application. Would allow you set a day to be closed without having to re-enter the time. Thinking of a school on spring break, they would set all the days as closed then reopen without having to setup each day over again.

Moved as duplicate #2487460: Closed all week

Posted by smd_ksu on May 12, 2015 at 5:46pm
If a business is closed all week the hours display is blank even with Show all days selected in the field display. The blank default behavior is understandable so there should probably be an option to select desired behavior.

See both linked issues for D7 and D8. It adds a 'comment' column to each time slot.
We can build upon that.

let's move this to the D8-version.

In the D8-version, we now have a hidden feature '#empty' => t('This location has no opening hours.'), in the formatters. We can add this to the settings page, and use it if necessary.

Issue #2860041: Cannot add comment when day is closed. is fixed.
You can now add a comment without a time.
Using the formatter setting "Group consecutive days with same hours into one set" , you can create 1 line for all week.

I guess the above change covers most of your needs.