The dashboard has views with sites that are all configured for business hours and are locked.
Release : 20.2
Component : IM Reporting / Admin / Configuration
The control at the top of the page is for the dashboard context. If not set to a site with business hours then no business hours can be selected/deselected.
Use a site as a dashboard context to but this will not impact the locked views.
Business hour priority order when applying filter to a view: