This feature is not supported with 3.x version. It will be available from Sitefinity 4.0. By design there is no API that allow you to create and manage additional page properties. Possible solution is using Navigable property of ICmsPage. You can set the property to false on a certain period of time using a ticker in your global.asax or just getting DateTime.Now value. We are working on a custom tool that will be posted on Sitefinity's Marketplace.
the Telerik team