I am interested to see other answers, but I would boil 90, and follow the rest of the hop schedule on time.
There will be some change in the utilization, but I don't know exactly what or how much. I suspect it will increase your bitterness somewhat, but that's it. I suppose it's possible that there is a curve regarding hop utilization being reduced after too much time boiling, but I would think it's well beyond an extra 30 minutes....