Hi!
The JMSS test consist of a prac report, information report, science reasoning, mathematics, and numerical reasoning. There are some guides on the old forums that you can check out.
It's not too late to start studying... I actually know some people who got in who studied the week prior but I highly do not recommend. If you start now, you should be fine for the test 🙂
For the interview, I have posted something on the "Jmss interview" thread.
If you have any questions, don't hesitate to ask!
Good luck!