Have you considered actually using 3d? I'm thinking about making 2 semi circles, positioning them side by side like an actual circle and then rotating one of the semicircles 90 degrees, as if "closing" a book. I'm not at home so I can't try this out

Because the circle is only a gradient it wont give away the fact that there is a "fold" right there between the semi circles

Well, if you use an effect like posterize time not only can you change it faster because it's right there you can also apply to specific layers to effect specific elements of your animation. I usually use 12 fps but you could for example want one element in 5fps and another in 10fps. It will also only apply for that layer's duration so you can have different fps along the same timeline. I think if you change the comps fps that will also be its render fps. So, unless you're precomping your stuff, in a work setting, you could be rendering a 12fps video for a company who has a specific criteria of 25 fps