In Modern and Ancient, you learn history. In Extension, you learn about history. There are schools of thoughts that argue history is merely a construct of what historians tell us. Others say there can be absolute, objective history.
How has 'history' developed over the years? There is a clear difference of how Thucydides conveyed 'his' history to that of say von Ranke. You learn about why there are differences and make judgements as to 'what is history' and how historical events/debates/people have changed our perception of history - for example, WW1 history in each country might be skewed by propaganda efforts of the time, but this is the history that we are taught, so is it actually "correct"?
The major project is actually just a heavily weighted assignment. You develop a question and perform an investigation into your topic. It's essentially your own construct and analysis of the historical events.
I didn't find it time consuming. Part of the course is evaluating and synthesising opinions/facts/debates/people/events. Master that and you won't find it time consuming.
https://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/history-extension-st6-syl-from2010.pdf
