RTX 4090 is equivalent to the performance of two RTX 3090ti, but RTX 4090 can only be used as a single card. He can only change the renderer, but the time cost of learning is the unknown. And the effect that comes out may be very different from the Iray renderer.
I think if a picture renders in less than 20 minutes, he is not waiting dry. He should be writing dialogue or planning the story afterwards.
I'm now rendering 4k resolution images in Blender in as little as thirty minutes tops. I can't go pose for the next image during this time. Only to plan the story and dialogue. Or Watch a movie.

It seems that Daz cannot run two at the same time. If it can work like this, LP can work with one RTX3090ti to render and another RTX3090ti to build scenes and character poses with Daz. Maybe he has two computers, and he's already doing like that.