This is the timestamp of when the node's call-setup rate (calls per second) hit its recorded maximum since the last reset. It helps an admin correlate a burst of new-call signaling load with a specific event, which matters because a high calls/sec rate stresses the node's call-processing logic differently than a high total-calls count does. For example, a spike timestamp coinciding with a known dial-up backup window would explain an otherwise puzzling signaling-rate alarm.