Judge John Cleland's eight-page memo and order said a postponement should only be a last resort and would require concrete justification.
"Absent extraordinary circumstances presented by either the commonwealth or the defendant, postponement of the trial date will only be considered if required by the demands of selecting a jury and providing for their care, conflicting demands on courtroom space, or similar logistical complications," Cleland said.
Cleland did grant Sandusky lawyer Joe Amendola three extra weeks to file a catch-all pretrial motion that had been due Thursday, and ordered prosecutors to disclose addresses and phone numbers of witnesses within seven days. He also adjusted other pretrial timetables.
"We will move forward with Jerry's defense, and we look forward to receiving additional discovery materials from the commonwealth," Amendola said in response.
A spokesman for the attorney general's office declined comment.
Sandusky, 68, denies allegations he engaged in sexual misconduct involving 10 boys over 15 years. He remains confined to his home while awaiting trial.
The former longtime defensive coordinator at Penn State founded The Second Mile, a charity for children where prosecutors claim he found victims.
Amendola had argued he needed the additional time to interview witnesses, subpoena records and hire experts.
Cleland said both sides agreed to the May start in early January, and indicated he was not persuaded by Amendola's "unsupported references to unidentified witnesses who might testify about unspecified issues."
"There is no assurance at this point that any delay of the trial to mid-July will not, in turn, give rise to subsequent issues prompting a request for still more delay. Delay has a way of begetting delay," Cleland wrote.
Also awaiting trial are Penn State athletic director Tim Curley and vice president Gary Schultz, both accused of lying to a grand jury investigating Sandusky and failing to properly report suspected child abuse. They have asked a judge to dismiss their charges, and no trial date has been set. Curley is currently on leave and Schultz has retired.
The arrests led the board to oust university president Graham Spanier and longtime football coach Joe Paterno, although neither was charged. Paterno died last month of lung cancer at age 85.
