FALSE: The real reason why someone may gain weight has nothing to do with the time of day. It comes down to total calories taken in vs. total calories burnt throughout the day. If you find that your schedule only permits to eat at 9pm or 10pm, do it! And yes, there may be more optimal times of day to eat certain foods depending on if you are active or not. But in the same sense, if you eat something 2pm and are not active, that food will partially be stored as fat for later use anyway just as the 8pm food. Just remember, your total calorie intake does not change just because its after 8pm!
I believe that the only correlation between the truth and this myth is that majority of people do NOT eat balanced and continuous meals throughout the day. This causing the metabolism to slow down and not stay at a steady state. And when you finally get home for dinner, you engorge yourself. The over abundance of calories in one sitting are not readily needed for energy and thus create weight gain over a period of time.