It should also be done at any point where your responsibilities change ie. you are training junior developers where you weren't before or people have left and n

It should also be done at any point where your responsibilities change ie. you are training junior developers where you weren't before or people have left and now you are the senior developer on a project. This is the best time to negotiate a raise because you were hired for $X to do Y and now you are doing Z so the pay should change to reflect this new job. I would also suggest that you treat any employment situation like an ongoing 6-month contract. After 6 months, figure out for yourself if the pay is still fair and talk with your employer about it. Basically treat it as if you were being hired for the first time. If you are not interested in continuing at that level of pay, then you should turn down continuing to work there. Of course, if you're happy then continue on.