This is the 704th most frequent German word.
tages
"Tages" is the genitive singular form of "Tag," meaning "day's" or "of the day" in English.
In this sentence, 'Tages' is again in the genitive case, used to describe 'Länge' (length), associating it with 'day'.
Die Länge des Tages variiert je nach Jahreszeit.
The length of the day varies depending on the season.
Here, 'Tages' functions to describe possession in relation to 'Highlight', showing that the highlight belongs to the specific day.
Das Buch ist das Highlight meines Tages.
The book is the highlight of my day.
Here, 'Tages' is used in the genitive case following 'des', indicating possession or association, specifically referring to the day in 'end of the day'.