I fly sparge and add the hops to my dry boil kettle. I've done 60 and 90min boils with FWHs and the results have been good in both cases. I almost always FWH at least some of my bittering hops nowadays, usually all of them. I perceive a better, smoother bitterness, but it's not scientific. Could just be me expecting smoother bitterness so I think I taste it. It's certainly not hurting anything, though.