Just to make sure I read the rules correctly: music have to be made within the given time, so no premade ones from for example Waterflame.

That's right — music (and all other assets besides logos, intros and fonts) must be made during the jam. Teams are allowed if you want to work with a musician during the jam instead of making music yourself.

If anyone needs music, I am available as a musician to throw together some quick ditties.