Summary: Exercise is recommended for the treatment and prevention of type 2 diabetes. Also, to control and reduce glucose fluctuations in people with type 1 diabetes. However, the most appropriate time and the most effective intensity of exercise is still unknown, and various studies provide different results and different recommendations, and none of the studies provide a comprehensive and practical result. We conducted our studies to examine the results and determine the effect of time and intensity of exercise on blood sugar control and glucose fluctuations during the day. Methods: search in PubMed and Google Scholar with keywords morning, evening, type 1 and 2 diabetes, exercise, interval, periodic, aerobic, and glucose and blood sugar fluctuations were performed. A total of 31 articles were reviewed and finally, 10 articles that were most related to each other or had complementary information were selected. Conclusion: HIIT exercises are useful for type 2 diabetes, but they are recommended for type 1 diabetes with less pressure. Morning exercise increases glucose and evening exercise is applicable for type 1 and 2 diabetes.