Have to say I'm a bit confused. I have exactly the Jobo 2300 as well.
No matter what dev, e6 or c41 I use I program the program I'm using, i.e., program 9, to the fill amount described on the specific tank I'm using, mine is 730ml.
NO TIME ADJUSTMENT!!!! Now, if the Jobo doc's suggest more then the 730ml for YOUR SPECIFIC tank model, i.e., 820ml then use that! Same if you are using the Duo Reel red tabs.
Again, the dev DOES NOT matter, follow the Jobo doc exactly and you will have a good day. The only execption to this rule is when running B/W's because of the different Devs and ISO's of course.
If you need further asst. please PM me.