Because his Christmas is so great, Timmy wishes that it was Christmas every day, but after fifteen days everyone gets tired of it because all of the shops are closed and they can't get what they want there. And because of Santa's Christmas holiday taking over, the other holiday mascots are jealous and vie for revenge.
Christmas is Timmy's favorite day of the year, as in addition to the tremendous amount of gifts he receives from Santa Claus, it is also the one day of the year he is guaranteed that his mom and dad will stay home and not have Vicky babysit him. So when the day arrives, he expresses through a song to Cosmo and Wanda that he wishes Christmas were every day. Despite their reluctance, they grant his wish.
At first, Timmy is thrilled to have Christmas every day, but things soon take a sour turn, as he begins to notice when he starts receiving less and less presents as each day passes. And because Christmas now falls on every day, all the schools, stores, and businesses remain closed, and everybody has become so sick of Christmas that the armed forces are working to shoot Santa's sleigh down. Even worse, the mascots for the other holidays (led by the Easter Bunny and consisting of Baby New Year, Cupid, and The April Fool) are furious that their respective holidays can no longer come.
Unfortunately, Timmy cannot reverse his wish, because every Christmas Eve, all the fairies in Fairy World transfer their magic to Santa so that he can make his annual journey, and they do not get it back till Christmas is over; but because it was Christmas everyday, Cosmo and Wanda cannot reverse the wish. The angry holiday mascots, planning to banish Santa to the non-existent date of February 33, kidnap Cosmo and Wanda (in order to use what remains of their magic against Santa's) and take off in the April Fool's bus.
Using a high-speed snowmobile, Timmy makes his way to Greenland, all the while getting help from other kids who celebrate Christmas, soon catching up with the holiday mascots. Disguising himself as another holiday mascot named Birthday Boy, Timmy tricks the mascots into letting him on their bus, then slows them down by puncturing their tires with Cosmo and Wanda's crowns. Up at Santa's workshop, the elves have gone on strike over the never ending Christmas, leaving Santa to come up with designs for rather pathetic looking toys. Timmy makes it to Santa's workshop in time to warn Santa of the oncoming attack (Mrs. Claus giving Timmy a lump of coal for making the wish in the first place), but the mascots soon catch up.
Santa's attempts to fight them off are futile, and his magic is soon sucked out of him and transferred to the Easter Bunny, who prepares to blow Santa to February 33 with an egg-shaped bomb. Timmy at this point arrives to stop this, but Easter Bunny is still willing to throw Timmy to February 33 for creating the mess he made and that he is the only kid that is there. Fortunately, the kids who helped Timmy in his journey show up, along with every other child with Internet access, and they help him make it clear to the holiday mascots that they do love their respective holidays as well (just not as much as they love Christmas). The mascots, realizing the error of their ways (as well as realizing they cannot harm children), give Santa's magic back to him, but it doesn't change the fact that it's still Christmas. Timmy then rallies all the kids to tell Santa that what they want is for it to be December 26, which they do. Thanks to that, the endless Christmas finally ends, and things return to normal. However, to make amends for the whole mess, Timmy, Cosmo, Wanda, and the other holiday mascots have to deliver the Christmas presents next year while Santa and his wife take a vacation in Hawaii and, to make sure no other kid makes the same wish Timmy made, Jorgen Von Strangle adds a new rule to Da Rules that forbids fairies from granting "Christmas Every Day" wishes.