Are you using Global Entry? If yes, then getting to pay duty is really pretty quick. If you do not have GE, then 2:50 can be tight even without duty. But have receipts, have payment ready, and there is a chance you'll just be waived thru especially if the items are for personal use. I came thru with 3 cases of wine once, declared, said I was drinking it 100% myself (hey it was great wine) and I was waived right thru. It's the liars who get stuck