Clip 1a: up to 4 s.
Clip 1b: 4 - 8 s and apply duration or time remapping for the slomo.
Clip 1c: from 8 s onwards.
You can razor the clips or use keyframes or use a copy from 4 -8 s, apply the slomo and replace the original. Many ways to achieve this.
I would try this in After Effects using Timewarp and Pixel Motion. In my experience, PP doesn't do the best job of slow motion, and at 10% it'll look like crap.