Indiana Code Title 35. Criminal Law and Procedure § 35-36-2-1

Sec. 1. When the defendant in a criminal case intends to interpose the defense of insanity, he must file a notice of that intent with the trial court no later than:

before the omnibus date.  However, in the interest of justice and upon a showing of good cause, the court may permit the filing to be made at any time before commencement of the trial.