Q: If Plaintiff files Amended Complaint late (Court granted demurrer w/ leave to amend), isMotion to Strike a good option

A: A motion to strike would not be the appropriate procedure, in my opinion. In California, a motion to strike lies against any irrelevant, false, or improper matter inserted in a pleading or when a pleading is not drawn in conformity with the laws of the state. (CCP 436.) A motion to strike might lie against the amended pleading once it is filed. The better approach would be to file a motion to dismiss under CCP 581(f)(2). Having said that, however, the decision whether to dismiss a case or not always lies within the sound discretion of the trial judge, even when an amended pleading is late, and a trial judge's decision whether to dismiss or not will only be overturned on appeal on a showing of abuse of discretion (the toughest civil appellate standard). (Harding v. Collazo.) A 3-day delay in filing an amended pleading may not strike a trial judge (who is used to delay upon delay) as being all that significant, particularly if there has been no prejudice caused by the delay. Keep in mind, in California, there is a strong, public policy favoring the amendment of pleadings, and the reason is because the law favors hearing legal matters on their merits. The policy favoring leave to amend is so strong that amendment must be permitted unless the adverse party can show meaningful prejudice which includes such results as the running of the statute of limitations, a delay of the trial, the loss of critical evidence, or added preparation costs. While I don't know the particulars of your situation, it seems unlikely that a short, 3-day delay would have caused such results, and in fact, the delay might be easily explained by many other circumstances. It could be inadvertence, innocent mistake, the party/attorney could be seriously ill, etc. You might want to find out why the amended pleading is late instead of rushing off and filing any motion. Good luck.