To inform citizens when they can use government services, governments publish the services' opening hours on their website. When opening hours would be published in a machine interpretable manner, software agents would be able to answer queries about when it is possible to contact a certain service. We introduce an ontology for describing opening hours and use this ontology to create an input form. Furthermore, we explain a logic which can reply to queries for government services which are open or closed. The data is modeled according to this ontology. The principles discussed and applied in this paper are the first steps towards a design pattern for the governance of Open Government Data.