Is it allowed to take part in this jam if I started the game a week earlier?
Hello. I think it's okay to use assets, sources and other packages you already prepared.
Bastiaan gave this answer on Discord:
The whole idea around the jam rules is that you don't bring a half finished projects into a jam and get a headstart on everyone else. Thats why a theme is involved and not announced until the start of the Jam. If you use some assets you've got lying around, I see no difference to that compared to a jammer who downloads an asset pack from kenney.nl for their entry
If you started a week earlier, to prepare your project, I think it's fine. You can also say it in your entry description, so everything is transparent.
It's a grey area, it depends a bit on what you did in that week, if its just general framework/setupwork I see little difference between that and using say the Godot XR Template. I think many jammers will take something they have already build as a base or copy stuff from existing projects to save time.
If you had been working on something for months and decided to reskin it to the theme, that would be a clear violation.
But after only a week, even if it is "half finished", unless you had prior knowledge of what the theme would be I don't really have a problem with it. Especially seeing that right now our jam is just for fun. If we had prices up for grab I might be taking a closer look at what "half finished" meant :)