A more thorough explanation:

The single-date-of-removal doctrine is a principle in civil procedure that sets a deadline for removing a case from state court to federal court. According to this doctrine, the deadline is 30 days from the day that any defendant receives a copy of the state-court pleading on which the removal is based.

For example, if a lawsuit is filed in state court and the defendant receives a copy of the complaint on January 1st, the deadline for removing the case to federal court is January 31st. If a later-served defendant seeks to remove the case to federal court more than 30 days after the day any other defendant received the pleading, the removal is untimely even if effectuated within 30 days after the removing defendant received the pleading.

The single-date-of-removal doctrine is based on the idea that all defendants must consent to remove a case to federal court. If a defendant has waited longer than 30 days to remove the case, they may not have the capacity to consent to removal.

The notice of removal is the pleading by which the defendant removes a case from state court to federal court. The notice must contain a short and plain statement of the grounds for removal and must include a copy of all process, pleadings, and orders that have been served on the removing party while the case has been pending.

For example, if a defendant wants to remove a case from state court to federal court, they must file a notice of removal in the federal district court in the district and division in which the suit is pending. The notice must be filed within 30 days after the defendant is served with process in the suit.

The removing party must also notify the state court and other parties to the suit that the notice of removal has been filed.

The single-date-of-removal doctrine and the notice of removal are important concepts in civil procedure that help ensure that cases are properly removed from state court to federal court in a timely and efficient manner.