Buffett will normally wait until the last minute to file anything with the SEC but this is constrained by his desire to release the annual report on a Saturday. The 10-K filing deadline for "large accelerated filers" is 60 days after the end of the fiscal year (http://www.sec.gov/answers/form10k.htm). This happens to be Friday March 1, 2013 if I'm adding correctly. So it is interesting ... will Buffett release the annual report on Saturday, February 23 with the 10-K following on Monday, February 25. Or will he release both the annual report and 10-K on Friday, March 1 even though that would break the habit of posting the report on a Saturday morning?

My guess is that he will go with March 1 for the 10-K and annual report since releasing after hours will still give shareholders the entire weekend to read the report and he won't be filing a week ahead of when he is legally required to do so. But I'm keeping both weekends open just in case.