Speaking of the Tulsa market, I remember the Beautiful Music station in the late 70s / early 80s (KBEZ, "Easy 93," 92.9 FM) going all Christmas possibly the week of Christmas? Christmas Eve morning? Not sure when... but then at 6pm Christmas Eve they would begin their "Festival of Music" which was commercial-free Christmas music from 6pm Christmas Eve to midnight Christmas night.
BTW, although they played the Percy Faith and so on, they also played Neil Diamond's (current at the time) Christmas album, same with Alabama, Barbra Mandrel, and a couple of others. (As a kid, I thought everything they played was OLD... only recently have I found out they were playing current stuff, too!)
I always used to listen for the last Christmas song right before midnight, and then listen to them go back into regular programming... it always felt odd to me for some reason... looking back, I have no clue how they could have done it any better...
In the late 80s / early 90s (but before they went alternative) Tulsa's "Hot New Z104.5" (KMYZ-FM 104.5 Pryor / Tulsa; top-40) was actually playing some sort of choral music in the wee hours of Christmas morning! I think by 10am Christmas morning they were back to their regular mix of Rock 40 and Christmas rock.
As I remember it in the late 70s / early 80s, stations of all formats were still mixing in format-appropriate Christmas music until Christmas Eve when they often would play syndicated specials of back to back Christmas music that started 6pm or midnight Christmas Eve and would run until noon, 6pm, or midnight Christmas day (usually noon or 6pm).
In particular, one of the local ACs (Magic 99) ran a special in the early 80s I think, called "A Special Christmas." It was hosted and ran for 12 hours... but they played it twice, so it ran 6pm Christmas Eve to 6pm Christmas day.