Phil in SF quoted Lessons in Chemistry by Bonnie Garmus
Six-Thirty was badly in need of a bath. Tall, gray, thin, and covered with barbed wire like fur that made him look as if he barely survived electrocution, he stood very still as they shampooed him, his gaze fixed on Elizabeth.
— Lessons in Chemistry by Bonnie Garmus (Page 139)
Oddly, i know someone else who named their dog Six-Thirty. Much much earlier than this book was published.