Only special Rockruff can evolve into Dusk Form Lycanroc. This special Rockruff, able to evolve into a Dusk Form Lycanroc, will be a given as a Pokémon Ultra Sun and Pokémon Ultra Moon early purchase gift. The special Rockruff can only evolve during the in-game time of 5:00 p.m. to 5:59 p.m. You can find out the in-game time from the barista at the café space in any Pokémon Center. To see the process of how to get Dusk Form Lycanroc in Pokémon Ultra Sun and Ultra Moon, check out the IGN video below:
Learn how to get a free, special Rockruff and how to evolve it into Dusk Form Lycanroc.