I wouldn't add whole oranges. For citruses in general, you want to use the zest only - that's the colored (orange) part of the peel. Some add it directly to their beer, I prefer to soak it in vodka for a couple of days first. I'd use the zest of two or three oranges for 5-7 days before bottling (add after fermentation is complete).
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Warrior's Ale II (w/exp 6300 hops)
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Supersecret sour beer experiment v0.5
Supersecret sour beer experiment v1.0
Supersecret sour beer experiment v1.5