Oh man, I had to learn the hard way.  I harvested a hickory middle of october.  Little bit of loosening to the bark.  Would have been pretty easy, should have did it in Sept.  Anyway, I got busy hunting so much I forgot about the 12 staves I pulled off.  Holy cow. I have working with these staves since Jan, trying to remove the bark, and its like die hard blue steel.  I think i am throwing sparks when I do it.  Also, on a few, I got dangeriously close to going into the first growth layer. 
Lesson learned.  Harvest and debark in the growing season.
Now, osage I keep hearing you want to do in Winter or checking is tough to control.