For elderly people with dementia or cognitive impairment, their biological clock can affect them by the time of day, according to Caring.com in "How to Deal With Signs of Sundown Syndrome."
Dementia can cause a person's biological clock to change. A common change? Becoming agitated or to suffer from other worsening symptoms at about the time the sun sets. This is called sundown syndrome. Elderly people and their caregivers should be aware of this problem, so any associated issues can be addressed.
The source of any increased agitation should be examined. For example, if there is a particular thing that upsets a person suffering from dementia about sundown that can be changed.
It might help with something as simple as serving meals earlier and perhaps affecting the biological clock.
Reference: Caring.com (February 26, 2018) "How to Deal With Signs of Sundown Syndrome."