My TA said Carnival has been horrible with their docs lately. I got mine two days before sailing in June. A friend I met on these boards got hers the day of departure. If things go normally, you should get them about 1-2 weeks before sailing.
Good news, I'm sailing on the 27th of this month and my tickets arrived today. So I would say around three weeks before. looks like they are not having any problems getting tickets mailed out on time anymore.