The Christmas Trees and Wreaths will stick around in the WG for most of December and are both breedable like regular plants, but if memory serves Christmas Stars aren't found there. They must be bred for by Poinsettia x Christmas Tree unless you already have some from previous years to breed to each other. Poinsettias are around all year long--they are regular plants and are breedable with each other all year, but only during the season can you breed them with Christmas Trees to get Christmas Stars.
So if this is your first year, you have to grow Christmas Trees to breed to Poinsettias to get Christmas Stars, so it takes 8-10 days for your first crop of Stars to be grown and 4-5 more for any bred Stars to grow up. If you have Stars already, you can just breed them to each other, so it's much shorter.
The Lucky Clovers only last a couple days right about New Year's Eve. Plan for that. I think the Fireworks are around when the Lucky Clovers are, but they might persist a few days further into the New Year (I'm not sure). Snatch both of these when you see them. Plan to have empty pots, you'll only get one round.