How soon can you send out Save the Date cards for an Anniversary Party taking place during a holiday?

Sending out the save the date cards with your Christmas cards is a good idea. However, are you sure you want to do this on a holiday? You might have a whole lot less people than you think. I wouldn't attend a party like that on a holiday, especially for something like a 5 year anniversary. 5 years isn't that big a deall to most people and it's really hard to get off days around New Years. I know that's why you're sending the save the dates so early but still I wouldn't bother for something so insignificant. Keep in mind they don't know you're renewing your vows. Also, dictating attire to guests is just wrong.