When to take the mock exam?

If you just got your MS in Finance, I would take the mock right away and see how poorly you did and realize what you need to hit the hardest over the next 3.5 weeks. Also, see 300 hours’s article on mock exams, you should take several, not just one.

The end for sure.  That’s a no brainer. 

I wouldn’t leave it too late, perhaps attempt it with 2 weeks to go before the exam. There’s no point in doing it JUST before the actual exam as then you have no time to go over the areas which you struggled with.

i would say two weeks is close enough to the exam that you should be 99% ready to take the real exam so you get to have a decent go at the mock, but you also have time to go back over the incorrect answers and actually learn from them.