California Code, Code of Civil Procedure - CCP § 1258.220

(a) For the purposes of this article, the “date of exchange” is the date agreed to for the exchange of their lists of expert witnesses and statements of valuation data by the party who served a demand and the party on whom the demand was served or, failing agreement, a date 90 days prior to commencement of the trial on the issue of compensation or the date set by the court on noticed motion of either party establishing good cause therefor.

(b) Notwithstanding subdivision (a), unless otherwise agreed to by the parties, the date of exchange shall not be earlier than nine months after the date of commencement of the proceeding.