This is a method of administering chemotherapy at certain times in the person’s circadian rhythm cycle so that the action of the chemotherapy is increased and the side effects are decreased. Not all drugs have been studied to determine their optimal administration time, but a lot have.
Here is a link to a review article from 2010 that explains (and shows the studies that had been done by that time).
And a consumer-oriented article explaining it far more simply!
That is an interesting idea! Glad someone is thinking that way…