Cioran's premise is correct, but he draws the wrong conclusion.
It is true that you will always kills yourself too late.
By the time you have reached a point where you prepare your suicide, things have escalated; had you killed yourself before, the escalation and the suffering associated with it would have been avoided.
The conclusion is bizarre.
Let us say that you are an adult who has never had the pleasure of learning to play a musical instrument, and you now want to make up for this negligence by learning the violin. It is a fact that at every point of time in your adult life it will be too late to learn the violin, since one should have started while being a child to achieve anything close to technical mastery. However, no one would draw the conclusion that it would be futile to start learning it at all; in fact, everyone would encourage you to start as soon as possible!
The same may be said about suicide.