It's quite possible that you've accidentally changed your composition to use the 3d ray-traced renderer instead of the standard renderer. That could make a huge difference.
I actually tried it both ways.
Actually the more that I think about it, I might have forgot to manually change my composition settings to 1080p. And if that is the case then it could explain some of the slowness if AE is trying to render out a scene with 16megapixel images. But even with that I wouldn't think that a 7 second scene would be looking at a 4 hour render time. (I did have Adobe Media Encoder rending what I had into 1080p though.)
If your comp is huge, that could certainly explain it.
Also, your assets should only be as large as they will ever be in the screen. That is to say, once you've got them clipped out how you want them in Photoshop, you should save a copy of the asset that have been resized down to 1920 wide or 1080 high max. Although, if you're planning to scale it up in AE or move the camera closer to it, adjust that number to whatever you need. Basically, the smaller your assets, the quicker AE will be able to work. (In most situations.)
I'll test it out tonight and report back. I just have a feeling that it couldn't explain the exhorbitant wait time. 4 hours for a 7 second clip is a little much.
Any feedback on my setup or settings?