In recent years it's begun after Halloween, around Election Day and definitely before Thanksgiving which I think is on 11/28 this year--fairly late. You can imagine the sales folks being anguished if there were some company prohibition of Christmas flips until after Thanksgiving--oh no! We can't do it till Nov 29? It's money, all money, and believe me I have seen folks on Facebook and Twitter light up at the very thought. "Christmas music (holiday/seasonal) is back on the radio! I love it!" So do the sales folks and owners who make big profits.
Yeah, some like me will turn away till it's a more appropriate time but they figure it makes money. (Cue Monty Python's Money Song here. "There is nothing quite as wonderful as Money." Maybe get it piped in, at stores.
Or so they feel.
Actual tweets from the listeners they covet:
>>You know it's that time of year when it's 28 degrees, & there's Christmas music on the radio. #LoveThisTimeOfYear
>>I love that it's 7am, raining, I'm on my way to the airport, & then CHRISTMAS MUSIC starts playing on the radio!

I love it!!!
>>I can't wait for Christmas music on the radio, holiday drinks at Starbucks, trees, Santa, decortations, and crowded malls
>>Just had an #Starbucks drink in a red cup! Heard a Christmas song on the Radio too xx

#EarlyChristmas
(There are anti-ones too, but see those above and you see why little dollar signs are lighting up the eyes of the station owners, etc.)
"Chri$tma$ has two S'x in it and they're both dollar signs." --Stan Freberg