In SharePoint Online the retention timer job is fired only once a week and only 2010 workflows can be started through this mechanisme. But with the new (in preview) service Flow it's possible to create your own timer jobs to schedule 2013 workflows on lists / libraries in SharePoint Online.
Start a logic flow from scratch and select the Recurrence option to start from (as the trigger).
Choose as action 'SharePoint Online - Create item' in a list at a specific site url.
Add a workflow to this list that will automatically start when a new item is created. From this workflow the processing of items in another list can be initiated.
Here is some inspiration to get this dirty job done:
- Looping Through Content in a SharePoint 2013 Site Workflow
- Workflow Loop Through Multiple SharePoint Items