Australian Brenton Tarrant's trial was due to begin on May 4, 2020, which next year will coincide with Ramazan in the Islamic calendar.
A statement released by the court said prosecutors were concerned the clash would pose a problem.
"A number of the witnesses to be called at trial are of the Islamic faith," it said.
Man accused of New Zealand mosque shootings seeks to move trial from Christchurch
It said a new June 2 start date for the trial had been confirmed after the defence raised no objection to the change.
The court is scheduled to hold a brief hearing on October 3, when it is expected to make a decision on a request by the defence team to move the trial away from Christchurch.
The South Island city was the scene of the worst mass shooting in modern New Zealand history on March 15, when Tarrant allegedly opened fire at two mosques while livestreaming his actions on social media.
Tarrant, a self-avowed white supremacist, has been charged with 51 counts of murder, 40 of attempted murder and engaging in a terrorist act.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ