The judge, James E. Boasberg for the U.S. District Court for the District of Columbia, said the case from the states needed to be dismissed because too much time had elapsed since the alleged offenses took place. The states, led by Letitia James, the New York attorney general, accused Facebook in December of buying up nascent competitors like Instagram and WhatsApp — deals made in 2012 and 2014 — to cement its monopoly over social networking. In a separate, 53-page opinion, he said the complaint by the Federal Trade Commission, also filed in December, failed to provide enough facts to back its claims that Facebook had a monopoly over personal social networking. The judge said that the F.T.C. had 30 days to refile its complaint. “This really stings,” said William E. Kovacich, a former chairman of the agency. “This is a reminder to those who have wanted a dramatic, sweeping litigation campaign to take on Big Tech that there’s nothing easy about it, because the courts have a different view of the antitrust system.”