There is no reliable way to determine when someone last logged on to Athena. However, a best estimate can be obtained by looking at AFS volume information.
A script called "lastlog" in the consult locker can easily do this for you:
The date listed in the output is when the user's AFS volume was last updated, which is most likely the last time they logged in.
If you omit the "-f" argument to add, the command will not work, because there is a similarly named yet different command called "lastlog" located in /usr/bin.