The Wiki page describes a design for a scheduler, which has not been committed to Solr yet (I checked). I did see a patch the other day (see https://issues.apache.org/jira/browse/SOLR-2305) but it didn't look well tested.
I think that you're basically stuck with something like cron at this time. If your application is written in java, take a look at the Quartz scheduler - http://www.quartz-scheduler.org/ -Simon
