I think with dried orange you want to do it at flamout. It needs to re-hydrate to get the flavor out, but it can also get lost if it cooks too much. Of course, make sure you have good sanitary handling with them as they are basically only going to get pasturized rather than boiled.
If you really want to get some fresh orange flavors, you might consider a tincture after fermentation. I've never done it on an IPA, but I have a Belgian that I use orange in.
My process is to use 2-4 oranges. I zest them and put the zest in about 1/2 cup of vodka for a week before I keg. Just before kegging in pour the vodka tincture unto the beer. (not the zest)
The most citrus flavor I've ever had I went one step further. I poured the tincture into the keg before racking. I then put the zest in a small mesh bag and zip tied it to the top of the out tube. This way it sat at the top of the keg and in the beer until I pulled off a couple of quarts of beer. I really liked the results of that. The only down side for me is that I cannot do a displacement purged keg prior to racking as I have to open it up to attach the bag. I have a batch of this beer in the fermenter now. I think I'm going to try this again. I will settle for just purging the keg a couple times before I rack.