I moved to the Netherlands in January 2013, because my husband got a contract to work in Eindhoven. I am currently in a recruitment process that started when I was still abroad. Am I still eligible for the 30% ruling?
Important is that the recruitment process started when you were still living abroad and that you will be able to proof that (for example an email discussion).
There is no formal rule which states that the employment contract must start within a certain period after arrival in the Netherlands or after the recruitment process started. But of course, the longer the period the more difficult it may be to convince the tax authorities that you came to the Netherlands for that job, especially if your husband also came to the Netherlands for a specific job and got the 30% ruling. Otherwise the tax authorities can argue that the main reason why you came to the Netherlands was to join your husband who already arranged an employment contract (which is of course an important reason too). And the longer it takes you to sign the contract which you were already discussing before you came to the Netherlands, the more the tax authorities may think that you did not come here on specific request of the employer in the Netherlands. That officially is not required too, the first step can also be taken by the (future) employee, but you want the whole picture to be clear and prevent questions from the tax authorities.
So there is no maximum period, but the sooner you will sign the contract the better.