As greetings, I think both "Advanced Merry Christmas" and "Advance Merry Christmas" are grammatically incorrect as well as semantically incorrect. Christmas is reckoned not as a single day but as a holiday season that lasts so many days, so when we say "Merry Christmas!", it's understood that our greeting applies to the whole season and not just to a single day nor just to Christmas Day on December 25 alone. To append either "advanced" or "advance" to "Merry Christmas!" is therefore unnecessary if not entirely nonsensical.
We must keep in mind that a Christmas greeting isn't the same as, say, a birthday greeting. Someone's birthday falls on just a single day, so if the greeting is being made a few days ahead of that particular birthday, it makes sense to greet that someone "Happy Birthday in advance!" If the greeting is being made after that birthday, it also makes sense to say "My belated warm wishes on your birthday last (date)." But it would be terribly unidiomatic if not totally out of line to greet someone "Advance Merry Christmas!" or "Advanced Merry Christmas!" before the Christmas season and "Belated Merry Christmas!" after the end of the Christmas season.
So today in particular, December 24, don't make the mistake of greeting someone "Advanced Merry Christmas" and "Advance Merry Christmas" simply because Christmas Day is still a good 4-1/2 hours away. Whether you say it in advance or on the day itself, just say "Merry Christmas!" and you couldn't go wrong with it.
(http://josecarilloforum.com/imgs/MerryChristmas_greetings-1C.png)