Civilian attorney John Henry Browne told The Associated Press that the date is too soon to give the defense team time to prepare, and they will ask the judge to reconsider. Browne had sought a trial in mid-2014.
"It's a very unrealistic trial date for us," Browne said.
Bales faces 16 counts of premeditated murder and six counts of attempted murder. He slipped away from his base in southern Afghanistan early March 11 to attack two nearby villages and returned covered in blood, prosecutors say. Most of the victims were women and children.
The Army is seeking the death penalty. Lt. Col. Gary Dangerfield, a spokesman at Joint Base Lewis-McChord south of Seattle, where Bales was based and where he is being held, said he could not immediately confirm the trial date.
Browne said the judge has scheduled questioning of potential jurors to begin Aug. 19, and dates for pre-trial motions to be filed and argued April 23-26 and June 4-7.
Browne and co-counsel Emma Scanlan have each traveled to Afghanistan to investigate the case, but Browne insists another trip by at least one member of the defense team would be necessary before the trial.
One hurdle to that is financial, he said. He has repeatedly noted that his firm is working for Bales for free - Bales also has appointed military defense counsel.
If Browne can't raise the money for another trip to Afghanistan, he said, his firm might have to withdraw from the case - which, he noted, could set the trial back more than a year.
Associated Press writer Rachel La Corte contributed from Olympia, Wash.