California Code, Civil Code - CIV § 1693

When relief based upon rescission is claimed in an action or proceeding, such relief shall not be denied because of delay in giving notice of rescission unless such delay has been substantially prejudicial to the other party.

A party who has received benefits by reason of a contract that is subject to rescission and who in an action or proceeding seeks relief based upon rescission shall not be denied relief because of a delay in restoring or in tendering restoration of such benefits before judgment unless such delay has been substantially prejudicial to the other party; but the court may make a tender of restoration a condition of its judgment.