if it has not been require for the exam, it would have specified as You will not be required to do so in the exam.
I meant if we does not requires to know how to derive, it would be specified in notes. For Example "However, this goes beyond the scope of Subject CT4 and you would not be expected to check the Hessian matrix in the exam."~page-44 CH-5. that means you should learn it. Edit:-if you really think that is wasting your time, you could know/mind asymptotic distribution of mu.