I see a delay after all packages are installed as well sometimes and I think this has something to do with post-install jobs that have to be done. How big is your boot partition?
I see a huge delay as well, and I think it's unrelated to %post. I've timed my kickstart file %post section and it completes within seconds, whereas it takes a long time (5m? 10m?) before it even gets to %post.
That's on a real machine, not kvm, though.