There are several things that can cause air to rise away from the surface of the earth. One, and probably the most common, is sunshine. As the sun heats the earth, some parcels of air become warmer than the air above them, and they begin to rise, similiar to a helium balloon rising in the sky. When it rises far enough, the water vapor condenses into visible water droplets, and we call them clouds. Another feature that causes air to rise, is mountains.
Air blowing against a mountain is forced to ascend.
It cools as it ascends, and if enough moisture is present, or it ascends far enough, clouds form. There are other conditions that cause air to rise as well. Each of these influences cause the air to ascend at different speeds. And the distance the air must ascend before reaching saturation is dependent on other factors, such as temperature and humidity. So, without knowing all these factors, it is difficult to determine the time required for air to ascend enough to create clouds.