A marker file is placed in the Ubuntu archive directory and is located: http://mirror.aarnet.edu.au/pub/ubuntu/archive/Archive-Update-in-Progress-mirror.aarnet.edu.au.
The trace file is located at: http://mirror.aarnet.edu.au/pub/ubuntu/archive/project/trace/mirror.aarnet.edu.au will have the timestamp of the last completed update.