Yahoo (NSDQ: YHOO) and Microsoft (NSDQ: MSFT) say in an SEC filing they will extend “the period to negotiate and execute” their search ad agreement, which they had initially said they would complete by Tuesday. While both companies agreed to the deal at the end of July, they said at the time that some details still needed to be hashed out. CEO Carol Bartz downplayed the development at the company’s analyst meeting, saying that the negotiations would not be extended for long. “We still have some papering to do, we still have some things to nail down,” she said. “Don’t be worried it won’t be consummated. The (letter of intent) is binding.” In the filing, Yahoo says “given the complex nature of the transaction, there remain some details to be finalized” but adds that the companies have “made good progress to date.”