Weekend Drawing Event is up in the top group of forums. Let me go get you a link.
That's to the All Media Art Events forum. Go in there and you'll see a thread with (DATE) Images Here. Those are the challenge images, posted on Fridays by the host. They can be from the Reference Image Library, their own photos or those they have permission for.
When you post your art from them, the challenge says post at two hours progress if it doesn't take that long to finish. Some people stick to that. I tend not to because I lose track of time and if it took more than 2 hours I didn't notice. But often it doesn't. If it did that usually meant waiting for paint to dry more than anything else.
Go ahead and read and comment on the threads. The rule people really stick to is to start ONE thread for all the ones you're doing from that WDE, and put MI in the subject line if you think you'll do more than one or have progress images so people know to check it more than once. I tend to work small and many times will do more than one reference.
Hosting is fun too and there's a perennial sign up for hosts. Great way to see many different versions of your loved cat by different people!