Today is Monday. Maybe 8 or 9 days ago I finished dry-hopping a 5-gal keg of IPA with an ounce of dried-on-the-bine whole cone summit hops + an ounce of pellet experimental lemon hops from Yakima Hops. Following a week of dry-hopping I squeezed the hop bag pretty well into the keg, and when I squeezed a bit more from the bag into a glass and tasted that I thought i would choke from the overpowering dank, earthy, oniony flavor of course from the summits. By this past Wednesday with the beer carbonated, the nasty hop flavor had permeated throughout the beer and I got a lot of that oniony/garlicky flavor and wondered if I had a dumper. However, by this past Saturday (3 days later), a lot of that nastiness was gone and the beer tasted pretty good. A friend who drinks plenty of IPAs came over this afternoon and we each drank a glass of it and it was very good, and we enjoyed it a lot and he said he got absolutely no onion or garlic flavor.
So in my very recent experience, this nastiness that comes from sulphur in dry-hopped summits disappeared quickly and completely, just with the passage of time and no copper added.