Strain it out. You are after the oils from the zest and those will have come out into the wort. After that, the zest is no longer needed.
I recently brewed a Saison and added the peel of 1 large orange and put it in the boil with 5 minutes remaining and then whirl pooled for 15 minutes before starting to chill.
I would not recommend using the zest from 12 oranges. Like I said, I used the peel from a large orange and it is noticeable. 12, I feel, would be way too much.
Just remember, you can never take out. Start low. If it's not enough, add a little more next time and adjust.