Departure

..... evenso did Odysseus rejoice when the sun went down, and he at once said to the Phaeacians, addressing himself more particularly to king Alkinoös: "Sir, and all of you, farewell, make your drink-offerings and send me on my way rejoicing"

Odysseus stays on Scheria for three days, so he leaves the island on December 15th. We can even estimate his time of departure:

The ship leaves Scheria after sunset. Odysseus doesn't wait until the party has ended, because there's lots to be done. After having made offerings to the Gods, carried the gifts on board and stowed them properly, they say goodbye. The fifty oarsmen take their seats and they leave the harbour.

Odussey Book 13 line 16-46 Samuel Butler

Odysseus seems keen to travel at night in order to arrive on Ithaca before dawn. He doesn't want his arrival to be known to the suitors, as he prefers to take them by surprise, so his escort to Ithaca turns into a kind of covert operation. Let's suppose Odysseus leaves Scheria on December 15th at about 21:00 hours.