You have to have an Own Tempo Rockruff AND level it up between 7-7:59 pm. One does not simply catch a Dusk Lycanroc.*
If you didn't participate in the event, the only way you can currently get an Own Tempo Rockruff is by breeding it. I do not know if you can make an Own Tempo Rockruff out of a Dusk Lycanroc, but I know if you had a Rockruff with that ability and bred with Ditto, you could make more back in Sun and Moon; I speak from experience. Whether that has changed for Gen 8, I do not know.
- I have actually seen people hack in Dusk Lycanroc raids before. I own a shiny one because of it. Keep your eyes peeled!
EDIT: Appears it's on Challenge Road and not, in fact, a hack. The source I used did not list this raid location, and I did not remember where said raid listed it!