If you take 24 and divide it by 3, which is Morning, Afternoon and Evening, you would get 8 hours. So each time of day lasts exactly 8 hours. So basically you could say Good morning at 4:05 AM, Good Evening at 8:05 PM and Good Afternoon at 7:59 PM. Taking into consideration that we all know that morning and afternoon are both separated at exactly 12:00 PM and that the whole day has 24 hours (almost 24 but the difference is already accumulated every 4 years on february).