First time ive heard of that, ive done mine in Bkk and Jomtien immigration and was told by the officers you can do it anytime from the first day you get stamped in.
You can apply for an extension at immigration from the first day of entry. So if you try to do that asap at least you will know, should be a formality though. They will give you 30 days from the date of expiry IE from 9th January .