The no eating after 8pm myth is a very common myth and one that I've even believed until recently. The myth states that if you eat after 8pm, the food you eat will turn into body fat. Your metabolism does not shut down at night. In fact, your metabolism can't even tell time.
Your body still needs fuel to repair itself during the night and if you workout later in the evenings, it is even more important. The key is to choose healthier foods such as lean proteins, good fats, and lots of vegetables. If you workout later in the evenings, don't be afraid to eat a meal, just make it a healthy one!