Well the thing about Entropia Universe is each planet is basically its own game and so you have to download each planet individually however you don't need to download them all and you can choose which planets you want, the Entropia Universe client its self is a pretty quick download so just download that and read about the planets and pick a planet you like and download that, the time really depends on how large and in depth the planet is.

http://www.entropiauniverse.com/download/