ATLANTA — Finishing a nuclear power plant in Georgia may take almost a year longer than expected, a government monitor said Tuesday in testimony that raises the possibility of a delay costing hundreds of millions of dollars. An analyst for the Public Service Commission, Steven Roetger, said the timeline for finishing two new nuclear reactors at Plant Vogtle is trending almost a year longer than currently scheduled. The first new reactor was supposed to be running by late 2017, followed by the second in late 2018.