>>53619616Rockruff actually has two forms: ones with the standard Keen Eye/Vital Spirit/Steadfast ability set, and one that only gets Own Tempo. The standard form can only become Midday or Midnight Lycanroc, while the Own Tempo ones can only become Dusk Lycanroc.
Because they're unique forms, you can't change their abilities to get yours to become Dusk, for instance.