Hi Alan,
I think the 40 hours would include discovery time and documentation time. The documentation is not too difficult: you have to create Javadoc, user documentation, and a document describing your design choices. Most of this you will be writing as you go along.
As for the essay exam - it is very simple. The purpose (as near as we can gather) is to provide Sun with some way of veryifying that
you developed
your submission. That is - the essay exam forces you to prove to Prometric that you are who you say you are (you have to provide identification to Prometric) and then asks you questions relating to the submission - if you did not develop the submission, you are not likely to get the answers right.
To give you an example, you might get an exam question like "did you choose RMI or Sockets for your network layer, and why did you choose it"? Obviously if you answered RMI when the real submission uses Sockets then there is something drastically wrong

.
[By the way - that is the only example question from the SCJD exam we allow to be posted here]
Regards, Andrew