I want a good parental control that allows to block desired website after e.g 2 hours of it usage.

Open DNS (http://www.opendns.com/home-solutions/parental-controls) has a couple and they are comparably priced to software solutions. This service dose not resolve DNS queries for the sites or types of sites you select. Like any other solution it can be beaten

Internet Filter (http://www.goldlimiter.com) has a duration lock option that does this kind of blocking.