SharePoint doesn’t officially support timer based workflows out of the box. Various hacks can be instigated to attempt to achieve this, and the most common one is to set up looping workflows that call other workflows. The drawback of this approach is that normally, at some point, the workflow looping breaks down and a user will therefore need to monitor, detect failure, clean things up, and then kick everything off again. True timer-based workflows can be approximated to some extent by SharePoint’s Information Management Policy options.
