I have an orchestration that is started by a public port published as service. Everytime somebody calls this service the orchestration starts

I need to start the orchestration every 30 minutes too.

Whats is the better approach? 
I've seen some [here](http://geekswithblogs.net/michaelstephenson/archive/2008/05/16/122203.aspx) but I would like something more simple