Time is not really a good measurement in this case. It was doing quite well until it was unfortunately nearly killed off by WW2. It's recent rise in popularity has been due to the tools people have been given to create and host various forms of media and learning platforms on the internet.
If you poll, you will find today that most people will not be aware of the concept of an international auxiliary language. This gives the adoption of one (not necessarily Esperanto) some kind of hope.
