There is no one answer to this that can be correct for every person. Each person has to make their own decision. Their decision can be affected by at least two main factors.
First, the length of time that you can hold out for a good job that pays the way you are accustomed to is based to a great degree on how badly you need the money. Let’s say that you have saved $500,000 and you do not have any kids who still need to be put through college. You are more likely to hold out for high wages than someone who has $50,000 in savings and has three kids that will need to be educated. So, each person’s financial situation will be relevant here.
Second, you have to take into account the way the job market looks. If you have been getting lots of interviews, you might hold on for a while on the assumption that you will get a job pretty soon. If people you know who are in your same line of work are starting to get hired, you could continue to hold out. However, if you are not getting any interest from “good” jobs and others like you are in the same boat, you should probably realize that it is time to settle for a job that pays less.
Thus, we can see that there is no specific time that is right for everyone. Each person has to decide based largely on the factors mentioned above.