I have implemented it for 0.9.4 this way:
* Page Date is set to the date the page was last updated
* Page Begin sets when the page will become available (and listed)
* Page Expire sets when the page will become unavailable (and not listed). By default Page Expire is set to 0 which means "never expires". Expiration of all existing pages upon update is set to 0, to avoid their undesired disappearing.
