Daniel Island-based software maker Blackbaud Inc. is extending its $275 million proposal to buy a Texas firm to give antitrust regulators at the Department of Justice more time to review the deal.

The buyout offer of Convio is being pushed out at least 10 days to March 7.

Blackbaud said today the move will provide the federal agency with "additional time to review information regarding the proposed acquisition without requiring a formal request for additional information."

"Blackbaud will continue to respond to any informal requests by the DOJ to provide additional information about its business and will continue to discuss the proposed transaction and answer any additional questions raised by the DOJ staff," the company said in statement.

Blackbaud offers a variety of software products to help nonprofits do their fundraising, marketing and finances. The company went public in 2004 and, in fiscal 2010, reported almost $30 million in profit on $327 million in revenue.

Convio is based in Austin and has 467 employees. It specializes in software that enables nonprofits, through email and social media, to keep in touch with their supporters and maximize fundraising. The company was founded in 1999, went public in April 2010 and now counts more than half the top 50 U.S. charities among its more than 1,500 customers.

The buyout offer was announced in January. Ay the time. Blackbaud chief executive Marc Chardon commented on the antitrust review, saying, "We're relatively comfortable that this is something that should get through the regulatory process relatively quickly."