Hang in there — I only got my invitation a couple days ago. They're still rolling out invitations at a steady pace. But, just as a side note, one of the first things they tell you is that they own the full copyright for any images you generate.
You definitely have to play around with prompts to get a feel for how it works and to maximize the chance of getting something closer to what you want.
When did you sign up? I just signed up, and it sounds like it takes a year to get access, probably longer now. It's a bit frustrating because I didn't sign up when it came out because I didn't need it at the time, but now I'm afraid of waiting a year when I do. These types of waitlist systems encourage everybody to sign up for everything on the off-chance that they might need it later. Wish they just went with a simple pay-as-you-go model (with free access for researchers and other special cases who request it), like how Copilot does it.
I signed up just over a month ago and from what I've seen, it looks like you won't have to wait more than two months to get your invite. A lot of people who signed up around the same time as me have already received their invites, so it looks like they're speeding things up and getting ready for a public launch soon.
I don't think the provider of an AI image generator service can decide they own the copyrights to it (perhaps they can require you assign the copyrights, though it may not even be copyrightable?), only courts can (and they decided the person setting up cameras for monkeys didn't own the copyrights to the monkey photos)?
Courts only decided the monkey couldn't copyright the photo (the PETA case).
The copyright office claimed works created by a non-human aren't copyrightable at all when they refused Slater, but that was never challenged or decided in court. It's not a slam dunk, since the human had to do something to set up the situation and he did it specifically to maximize the chance of the camera recording a monkey selfie.
If I set up a rube goldberg machine to snap the photo when the wind blows hard enough, how far removed from the final step do I have to get before it's not me owning the result anymore? That's the essence of the case, had it gone to court, probably the essence here too.
My guess is the creativity needed for the prompt would make the output at least a jointly derived work regardless of any assignment disclaimers--pretty sure you can't casually transfer copyright ownership outside a work for hire agreement, only grant licenses--but IANAL and that's just a guess.
You definitely have to play around with prompts to get a feel for how it works and to maximize the chance of getting something closer to what you want.