For WCM content, you can define an effectivity period (start date / end date) that controls when the content gets promoted to the staging sandbox (and hence becomes eligible for deployment). This isn't quite the same thing is scheduled deployment, but if you've configured auto deploy (available from v2.2 onward) then in practical terms it ends up being the same thing.
Note that with this model, undeployment is still manual - the end date is a reminder rather than an automatic action; it serves to "poke" the author and remind them that something (eg. deletion) needs to be done with the content.
If you require true scheduled deployment, you might find the "wcm-deployment" project on the forge relevant (http://forge.alfresco.com/projects/wcm-deployment/). It includes a Web Script that can be invoked via wget from cron, and the intention is to implement the same functionality as a Quartz bean as well (so that it can be scheduled from within Alfresco via the Quartz timed job execution engine). I just haven't had time to do that yet. :wink:
