My experience is they start off with Angel Drop and probably Limelight (possibly cut down to 'half trail') in Dec. They may put snow down on the blacks but they delay their opening a bit. The big green slope has to be open and the bunnies. anyway, it changes a bit every year but it seems like Jan they start to put everything else up. I suppose it depends on a variety of factors -- but also crowds which tends to be a little sparse until after x-mas.
SO if you go up and think you can enjoy 4 hrs of going up and down the same trail, I'd say go for it -- although repetive, if you take the non-stop ski from trail to lift attitude, you can really get in a lot of skiing and be home in time to wrap packages, make egg nog and practice your carroling.