Clouds form because of rising moisture getting to a certain height and condensing. Reduce the evaporation, and the clouds stop forming. Thus clouds start to form as the day warms up, and stop forming, indeed disperse, as it cools down. Of course it is more complicated than that because of clouds blowing around and winds and parcels of warm air and cold air and depressions and anticyclones all that, but on a small scale when overriding factors don't apply, it can work in that simple manner.