From what I've seen, if you're in the middle of learning a skill, the encyclopedia lists the skill as being 0s long, if you haven't learned it yet, it shows however long it would take you to learn it, and after you've learned it, it shows you the actual base learning time for the skill. Personally, I'd like the encyclopedia to list base learning times and the skill table tell you how long it would take for you to learn it. :/