This pretty much - you should try to make your study goal oriented as opposed to being time oriented.
To be honest, I have never really understood the whole logic of slacking off in year 11. Yes, year 11 doesnt count - but putting in the effort then helps you to develop study strategies which you will need for year 12. I mean, if you were a football player and you had a Grand Final in two weeks, would you say "Ohh, who cares about training, it doesnt count I will just try on the day". As the old adage goes "Battles are won before they are fought".
In saying that, there probably are a few people who can bludge year 11 and then do well in the HSC - but I think they are in the minority (when I say bludge, I mean really bludge as in do nothing, not the BoS version of "bludge"). When I was doing the HSC, quite a few people came out of nowhere during the first two terms of the HSC, but died off around trial time. The people who stayed consistant and were on top at the end were the people who had put in the effort in previous years. Personally, I dont think I would have done nearly as well if I hadnt put in effort in the earlie yearsr.
However, whilst you should put in the effort in year 11, you shouldnt be killing yourself niether. With school, its not the work that will get to you, but the stress and pressure. So yes, put in the work, but dont stress too much about results and stuff for year 11.