When dealing with a wide variety of people and experience, you have to set an expectation that seems reasonable to the majority. Setting unreasonable expectations just creates frustration and leads to simply ignoring the policy as unattainable. I see you are from the Denver area, and the course I'm referring to is Foothills. I know from many years of play that 4 hours is not unreasonable as long as everything goes well. 4 hours becomes difficult to impossible when a group experiences a few problems with lost balls or other issues which can cause slower play with casual golfers.
In the Men's Club, we have the added inspiration of the penalty threat to keep us focused on pace of play, but casual players need a different form of reinforcement. Putting out those clocks, and setting them to an achievable goal, is a better, more positive way of getting buy-in from the general public. Nothing says that once players are used to playing to the clock that it can't be gradually adjusted for slightly shorter rounds as time goes on.