14. January 1, 1968
Bellatrix is in charge of them on the first day of the new year, and Narcissa is sitting quiet downstairs, but Andromeda did something to make Bellatrix angry, and Sirius knows when Bellatrix pulls out her wand that he has to get out. He knows that she didn't really mean it, how could she, they're family, but that doesn't stop him from padding out of the room.
He ends up in a closet where Kreacher keeps the linens, and doesn't come out for a few hours.
When he finally does, no one seems to have noticed that he was gone.