A campaign begins with the first New Day Phase. The players did not set the Day Dial during setup, so they set it to 1 now. Additionally, Black Marsh’s province effect says that at the start of their first day in Black Marsh, the players must place a overland token on the Sunny weather spot on the weather gauge at the edge of Black Marsh’s overland map. They do so, then move on to the Overland Phase.
Adventurers must spend their first day in their starting town, so the party remains in Lilmoth during its first Overland Phase, which triggers a town encounter that must be resolved in the Encounter Phase.