Hard to say without knowing the AA%'s, but putting the extract in at 60 would mean about 20 IBU and at 15 min. about 40 IBU, if the Centennial is around 12%.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk