Any time, and the common assumption that icebergs are an early season thing is wrong. Icebergs last for years. They drift around the continent slowly sculpting down, so a March trip has no shortage of them. The late season iceberg graveyards at Booth Island, Port Charcot and Pleneau are among the most striking ice you'll see all year.
This matters because the belief costs people money. Someone books peak season partly for the ice, when the ice was never the variable.
On the blue ice question, since it always comes up: the blue comes from compression squeezing the air out. It reads strongest on overcast days, which is the opposite of what most people expect and a useful thing to know before you write off a grey morning.
Which graveyards you reach depends on ice conditions and your itinerary, so nobody can promise you a specific one.