Rearranging the letters of 'O Christmas Tree' (Christmas carol) gives:
Orchestra times!
(by Mark McNamara using Anagram Genius) (2008) (pending approval)
Other related anagrams without their own page:
"What gift from Santa would you like to see under the tree on Christmas?" -> "True wit, harmony, kindness, calm, rest, good future, seat, health, wife too." (by Aronas Pinchas using Anagram Genius) (2008) (pending approval)
""I wish you a Merry Christmas!"" -> "Rich is as yummy as worthier." (by Maria Cecília using Anagram Genius) (2006) (pending approval)
"Merry Christmas and Happy New Year" -> "Starry hype. Many wrap merchandise." (by Mike Mesterton-Gibbons by hand) (2002)