Ragna is the easiest to do on and yes the timing is slightly different for characters. What you want to do is first of all, let 5C hit twice. Then you have to delay 4D~A so when you hit with 4D~A you hit near the front of Ragna's stomach and not under his legs. If you hit it under his legs, you have to delay the j.8D~A and/or Jakou.
http://www.youtube.com/watch?v=axraUUC-R1U#t=10s
As you can see here.