I have had several customers experience the PowerPivot "scheduled data refresh" running over and over when setting the Schedule Details to Monthly and choosing a Day.
As you can see below, the refresh runs over and over; it's stuck in a loop. In this case every 5 seconds. If the Data Model was larger and required more data to refresh, the duration would be longer.
We were able to fix this in the below CU:
Cumulative Update 4 for SQL Server 2012 SP2
FIX: Continuous refreshes occur after you configure scheduled data refresh in PowerPivot for SharePoint 2013
Run the "PowerPivot Configuration Tool" after Upgrading the Analysis Services POWERPIVOT Instance.