I'm sorry, but the suggestion that 2-3 hours will suffice is really disrespectful to this memorial. We allowed a full day to visit the memorial and the new observatory and never made it to the observatory. The 9-11 Memorial simply commands more attention than a passing glance and you will find that you are drawn to read the notes, the personal testimonials, the memorials, the histories of individuals... There are literally thousands of stories ensconced in this memorial and it is not possible to visit each part of the exhibit in a short 3 or even 4 hours. That being said, if you have only a few hours, by all means, go and see all you can. It is worthwhile for everyone to appreciate the reality of those events and while it is a very sobering visit, it will also show the courage of many who met the challenge that day.