Sundowner Rounds and Sundowner Leagues in Golf
Such tournaments are often part of a golf league's weekly schedule. Sometimes the term "sundowner" is applied to such leagues themselves, as in a "sundowner league." In other words, if a golf association sets a slate of tournaments that are scheduled to begin in the late afternoon, it might call such events "sundowner tournaments" or refer to the whole schedule as a "sundowner league."
You'll most commonly find such events scheduled during the summer months, because the sun sets at a later time. That makes sundowner tournaments that begin after golfers get off of work a possibility in some locales.
"Sundowner tournament" and "twilight tournament" are interchangeable terms, with "twilight tournament" being the more common term.
"Sundowner" can also apply to an individual golfer. A golfer who gets up and tees off at the crack of dawn is a "dewsweeper." One who tees off late in the day and finishes as the sun is setting is a "sundowner."