One should eat dinner approximately four to five hours after eating lunch. If that falls in the 5 p.m. to 6 p.m. window, then you should have your dinner at this time only. Eating before bedtime can hinder your sleep and therefore, it is advised to eat before 2-3 hours of sleep. Eating dinner early offers your body enough time to stabilize blood sugar levels, which plays a role in making you feel less fatigued and irritable. It will also prevent you from gaining weight.