Hi Tim
I had to call this time last year for Xmas Day ADRs (inc CRT).
Did the usual - start dialling at 11:57 UK time, hitting redial when you hear the "our offices are closed" spiel and got through at 12 on the dot. Was on hold for about 13 minutes I think, but I still got CRT (with a choice of times) & Yachtsmans Steakhouse for dinner (which we later changed to Cali Grill which still had ressies about 3 weeks later).
I dont think you will have any trouble getting Ohana, but Le Cellier seems REALLY popular right now (deservedly so) and still worth calling at noon on monday for if you want to eat here Xmas day. In fact ALL the World Showcase restaurants were fully booked for the week of the 23rd Dec thru New Year last year (a helpful CM at Le Cellier told me that !!). They had a few late spots at Marrakesh, but that was it for the whole week! Book EVERYTHING you think you even MIGHT want to visit!
Good luck!!