I don't know how to show it in the CLI, it's not in the output of show interfaces verbose or show port-statistics afaik...
Another option could be to query it using SNMP. Avaya supports the IF-MIB, and the ifTable entries contain an ifLastChange value (.22.214.171.124.126.96.36.199.1.9):
The value of sysUpTime at the time the interface entered its current
show interface history
To display histograms of interface utilization, use the showinterfacehistory command in privileged EXEC mode.
show interface [ type number ] history [ all | 60sec | 60min | 72hour ] [ both | input | output ]
(Optional) Interface type.
(Optional) Port number of the interface.
(Optional) Specifies ...