Outlook.com Sweep Feature...

Quick question for those who've used hotmail/outlook longer. The Sweep Feature seems to be a great way to keep my inbox clean without having to manually delete everything. Just create rules to keep the latest version of my Grey-Mail and have the rule delete the rest.

My question is, does anyone know when exactly outlook.com actually runs the rule? Is it daily? It doesn't seem to be when object arrive. There doesn't seem to be an option to control when the rule runs like on Office Outlook.