There's around sixteen freights a day plus two passenger trains most days. A few hours either side of sun rise should coincide with a group of northbound and southbound freights...perhaps four or five trains. But you should see at least one train every two hours or so throughout the day.
Thanks Sulla1,
I did manage to get what I wanted and fortunately the day I went to get it there was a failure of the Fitzroy level crossing and so the section between the marshiling yard and the crossing point to the north required use of train authorities and made the scanner come alive with valuble info re trains, directions and times.