Dawn and evening are the unique periods of the day. While lighting from the sun is similar, the atmosphere is different. When you combine human emotions with that, the difference is felt in the mind and the body. Evening is when people come back home after the hard day of work, and ready to unwind, may be with a glass of wine or beer.
At dawn, we have just woken up after a good night sleep. We don’t need any stimulus except for what we get from the nature. Sun has not yet come out, but some light has spilled from behind the horizon, and has blended with the darkness of the night that is about to disappear. There is hardly any traffic on roads to create various kind of pollutions. When that happens on the bank of a river, and in presence of beautiful trees and greenery, the atmosphere can’t be replaced by any stimulus.