Cal. Code of Civil Procedure § 2034.720

The court shall grant leave to submit tardy expert witness information only if all of the following conditions are satisfied: (a) The court has taken into account the extent to which the opposing party has relied on the absence of a list of expert witnesses. (b) The court has determined that any party opposing the motion will not be prejudiced in maintaining that party’s action or defense on the merits. (c) The court has determined that the moving party did all of the following: (1) Failed to submit the information as the result of mistake, inadvertence, surprise, or excusable neglect. (2) Sought leave to submit the information promptly after learning of the mistake, inadvertence, surprise, or excusable neglect. (3) Promptly thereafter served a copy of the proposed expert witness information described in Section 2034.260 on all other parties who have appeared in the action. (d) The order is conditioned on the moving party making the expert available immediately for a deposition under Article 3 (commencing with Section 2034.410), and on any other terms as may be just, including, but not limited to, leave to any party opposing the motion to designate additional expert witnesses or to elicit additional opinions from those previously designated, a continuance of the trial for a reasonable period of time, and the awarding of costs and litigation expenses to any party opposing the motion.