Richard Schulze wants to see Best Buy‘s holiday-season sales performance before he and his backers decide how to handle their potential bid for the consumer electronics chain. He and the company said today that they’ve extended the agreement from August that enables Schulze to see confidential company information: He now can make a proposal sometime in February, and the board would have 30 days to respond. The news sent Best Buy shares tumbling more than 15% this morning, reversing yesterday’s gains after the Minneapolis Star Tribune reported that Schulze was preparing to offer as much as $6B for the company ”by the end of the week, possibly on Friday.” Under the amended agreement with Schulze, Best Buy says it will extend the deadline — to March 15 from February 22 — to notify investors of shareholder proposals ahead of the 2013 annual meeting. Best Buy plans to announce its holiday-season sales January 11, and report Q4 earnings on February 28.