If you are in your twenties, 2 times 9 is 18, that is, 10 days, it is normal for 8 couples to live; Over 30 years old, 3 times 9 gets 27, that is, married 7 times in 20 days, about once every 3 days; If you are over 40 years old, it is 4*9=36, which means about 6 times every 30 days, once every 5 days on average, and so on!
Under normal circumstances, if both sides have no physical problems, the time for one time is about 5~ 10 minutes. Why is it a general range? This is mainly because there are individual differences in husband and wife's life, and it is not completely guaranteed that everyone will stick to the same time. Of course, men can't stick to it too short. If there is not even a minute, it may be a real problem.