It is better to review in time than to postpone it, but the sooner the better. The best time to review depends on one's study habits and the nature and difficulty of the course. Listening to lectures is more demanding, there are many problems, and it should be timely; Basic understanding in class, review is only a time of in-depth study, every one or two days, the impact is not great. The concepts and principles of the course are abstract and confusing, so review should be timely; Lectures are mainly narrative contents, which are consistent with the contents of books, and can also be reviewed at intervals.