Lycanroc-Dusk spawn during... well, dusk time, and wherever you can find Lycanroc, so in:
North Province of Area One, East Province of Area One, South Province of Area Two, South Province of Area Four, South Province of Area Five, South Province of Area Six, West Province of Area One, and Glaseado Mountain. Source: Lycanroc's page on this website.
N.B. They also spawn in the Great Crater, but only as Midday Form.