Research has shown 1 week to complete for a long, long, time.
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For many months now. I noticed this just after surveying an anomaly that gave me 25% of my research. It started at 6 weeks to complete and stayed there for quite a time. Then I successfully surveyed another research anomaly and it changed to 3 weeks, and remained there for many months. After a while, it dropped to 2 weeks, tnen after anohter many months it dropped to 1 week.