About an hour before the agreement was due to expire Friday, Georgia Power issued an 11 p.m. statement saying it had been extended.
The utility owns a 46 percent stake in the project, which is billions of dollars over budget and years behind schedule.
Company officials say they're still studying costs and a timeline for several options, including taking over construction of both nuclear reactors, canceling one or canceling the project altogether.
Westinghouse Electric Co., the U.S. nuclear unit of Japan's Toshiba Corp., filed for bankruptcy in March.
Company officials said this week that about 6,000 people are working at the Plant Vogtle (VOH'-gohl) site south of Augusta.