When is the right time to negotiate salary? Is it after the probation period?

Immediately after the interview, when the candidate passes it. 

This will all be spelt in your contract. It is not a good idea to negotiate the salary after probation end. Give it at least one year before you ask for a raise (in addition to automatic salary increase in your contract).

It depends.  You can discuss that before the probation saying if I pass the probation then I will get this raise ?.  But I dont think it is a good idea to do it after the probation because the company would not like it.

Hello, surely not before or after the probation period, having a raise is not given it is earned by your performance at work, it could be a unique act of quick profitable thinking or a small act of ethical behavior that will be noticed by any higher rank in the company this might take time certainly not before the probation time it also might take in some companies more than one act of loyalty. regardless an employee should always by in good standing and having a positive thinking about the work they do and not just expecting nor waiting for a raise only.