No experience with this in the corporate world (the visitor spaces have never had any time limit, although we have had emails from management that there were employees in visitor spaces and they needed to move their cars, with nebulous threats of dire things happening if they weren't moved), but we have assigned spaces in my subdivision and strict rules for how long visitor spaces can be used by a single car. If you are a visitor and get caught parking in a resident space, or if you are a visitor who breaks the visitor space rules, your car gets towed. We're not as strict as some though. One of my friends growing up had to have their license plate(s) registered with management, and each unit received a certain number of visitor passes. They had security driving through the lot on an hourly basis. If you were visiting, you had to put a visitor pass in your windshield by the second time security passed by or you would get a warning "ticket" placed on your car and your license plate would be noted down. The "ticket" would act as your visitor pass until it was removed or 24 hours had passed. The second violation would result in your vehicle getting towed.

I agree that you wouldn't want to tow an important customer's car, but if they are going to insist on a two hour rule, there needs to be consistent enforcement to prevent employees from using the spaces (registered tags for employees), but have something in place for customers who, by necessity, are going to be there more than two hours (visitor passes or registered tags).