How to pause a server for a time period when an entity arrives?

I'm trying to model a physical device that can operate on a fixed number of work items at a time. Each work item must be worked on for a fixed amount of time. The device is paused for a fixed amount of time whenever a work item is inserted or removed.

I currently have an N-Server to model the device and am looking at using the service control pause input but I can't figure out how to generate a timed pulse signal whenever an entity enters or leaves the server. How can I generate this signal?

Is there a better way to pause the servers when entities enter/exit?