Hey Benjamin,
If you pre-comp your transitions between your frames, then add markers to each final position (ie. page1, 2 etc)
Then in your main comp, apply those markers to your PreComp (Just add a layer marker, right click and select ‘Update Markers From Source’).
Then, add your slider, and add the below expression to TimeRemapping, and repeat the pattern until you get your 12.
Just make sure your last value in if else (what’s 5.001 in this example) is anything higher than 12, otherwise it might break.
NB. this expression has the Slider starting on 1. So 1 for page/frame 1.
Does this make any sense? Apologies for the messy expression.
s = effect("Slider Control")("Slider");
p1 = thisLayer.marker.key("Page1");
p2 = thisLayer.marker.key("Page2");
p3 = thisLayer.marker.key("Page3");
p4 = thisLayer.marker.key("Page4");
p5 = thisLayer.makrer.key("Page5");
L1 = linear(s,1,2,p1.time,p2.time);
L2 = linear(s,2,3,p2.time,p3.time);
L3 = linear(s,3,4,p3.time,p4.time);
L4 = linear(s,4,5,p4.time,p5.time);
if (s > 0.999 && s <1.999) {L1
} else if (s>1.999 && s<2.999) {L2
} else if (s>2.999 && s<3.999) {L3
} else if (s>3.999 && s<5.001){L4
}