Chief U.S. District Judge Michael P. Mills set the new date after a request by Roy Percy, who represents defendant Joshua Brandon Pillault.
Pillault, 20, faces two counts that he planned to injure and kill people, as well as destroy the school in an attacked allegedly planned for the April 2013 anniversary of the 1999 massacre at Columbine High School in Colorado.
He pleaded not guilty to the indictment Jan. 16.
Prosecutors claim Pillault, who attended OHS but did not graduate, made attack claims over the Internet using a pseudonym traced to his mother's home in Oxford.
If convicted on all charges, he faces up to 15 years in prison and $500,000 in fines.