I would add that the type of solution determines where the hydrolysis takes place.
With an anhydrous solution, all the water must come from the humidity int he air. As Francisco mentions, the rate of reaction is relatively slow since the concentration is low. This can however, lead to a perfectly adequate film with excellent optical and mechanincal properties. The slow reaction rate provides ample time for the film structure to form. I have found this to be best for titanium based films.
A completely hydrolyzed solution does not need any atmospheric moisture. sometimes drying is a problem. I have found this to be best for silicon based solutions.