Hi there,
Actually I am the developer who recently added this feature to PaperCut - allow quotas to be scheduled for shared accounts. This should be able to fulfill your requirements. This feature is available in version 10.2 or higher (currently latest version). More details about how this feature works in the release history here:
PaperCut NG - Release History
If you find a bug in this feature, it's all my fault. :-)
Cheers,
Priyanka