This sounds like a question that must have come from something your teacher said in class. It is certainly not common to say that Reconstruction failed because of its timing. I suggest that you look at your notes to find the answer.
If I had to answer this question, I would say that the problem with the timing of the Reconstruction Era was that it came too soon in our history. It came at a time when there was very little support for the idea of African American rights across the country as a whole. Because of this, Reconstruction failed to improve the lot of African Americans as much as it should have.
Reconstruction was meant largely to force the states to start to respect the rights of the freed slaves. However, it failed to do this, largely because most Americans did not really care about this issue. This was a time in the United States when very few whites were interested in helping African Americans. Because of this lack of interest, the North was not willing to do what it took to force the South to set up a system of laws that would actually respect and protect the rights of African Americans.