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I may be generalising: a lot of people do this subject for the mark-up, without the ability to cope with the harder maths concepts. (The fact that Specialist is the only non-LOTE subject that can be scaled to over 50 is tempting in itself.) It is possible that the students you asked about the difficulty of Specialist fall into this category.
The key thing with this subject is that most of the topics are new to the students, or alternately new techniques under old topics are introduced (an example is linear approximation under integration).
Therefore in my opinion, it is essential to do as much practice as possible through exercises and worksheets, in order to understand and master these concepts. If you are a reasonably high achieving maths student or is a a person who is prepared to work hard, you may want to consider doing Specialist.
But since I am in year 11, I can not shed some light on the recommended hours spent on Specialist per night. It also depends on the individual. Some will find Specialist a challenge, some will ease through it. But its not what's underneath you, but what you do that defines you.
Hope that helps, Trent.