Your pores are not as open because you've been sleeping all night. During the day you were moving around increasing blood flow, perspiration ect. The skin rested and closed it's pores making a smoother surface. I'm not real sure about this, It's an educated guess.
This is because your skin is regenerating itself in the night. Dead skin cells shed off and a fresh layer is formed making it softer and smoother.
possibly because your skin replenishes itself while you sleep?