Any party may make a demand for an exchange of information concerning expert trial witnesses without leave of court. A party shall make this demand no later than the 10th day after the initial trial date has been set, or 70 days before that trial date, whichever is closer to the trial date.
Source:
Section 2034.220, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=2034.220..