This TimeStamp reports the value of sysUpTime at the time of the most recent management-initiated change to this particular collector's row in tmnxIpfixExpPlcyColTable. An admin uses it to see when settings for one specific collector session, such as its MTU or admin state, were last touched, distinct from changes to other collectors under the same policy. For example, an admin troubleshooting a stalled export to one collector checks tmnxIpfixExpPlcyColLastCh to see whether that collector's row was recently reconfigured.