Timeframe: Indiscriminate (No spoilers).
Disclaimer: I don't own Chuck. Or Christmas. Though I suppose by this point, Christmas is public domain. And since I am a Christian, I guess I can lay claim to it. But I still don't own Chuck.
"Merry Christmas, Sarah. Here."
"Oh, Chuck! These earrings are beautiful! I can't give you your present until later, though."
Chuck, assuming something spy-related that she couldn't give him in front of Ellie and Awesome, nodded.
In Chuck's bedroom, Sarah reached into her overnight bag.
Turning around, Chuck saw two stickers on her white sweater: "To: Chuck, From: the CIA" and "Do Not Open Until Christmas." The word "Night" had been added.
Just before nodding off, Sarah, wearing only her new earrings and a gigantic grin (matching the one splitting Chuck's face), whispered in his ear, "Merry Christmas, Chuck."