Question

explain the reason between advanced sunrise and delayed sunrise

Answer 1

due to atmospheric refraction of sunlight. An observer on the earth sees the sun two minutes before the sun reaches the horizon. 

Answer 2

Sun can be seen about two minutes before actual sunrise because of refraction of sunlight through the atmosphere. When the sun is just below the horizon, sunlight enters the earth's atmosphere obliquely and gets refracted through the different layers of the atmosphere. As a result of this, sunlight gets bent and reaches the eyes of an observer. Following the path of the light rays entering the eyes, the observer sees the sun slightly above its actual position. As a result of this, sun can be seen about two minutes before the actual sunrise