The stave I just roughed out was cut last fall I believe. The ends, handle and tips are sealed.
How long should I wait before I start working it?
Just to be on the safe side Jim, probably a good idea to seal the back also.
That bark is pretty efficient at holding moisture in. Where did you have it stored? I've got one in similar shape right now and I thought I'd wait til fall before jumping on it. But for yours, I'd give it several months at least under the proper conditions to make sure any use of heat (for straightening or reflexing purposes) doesn't cause any checking.
But as far as Osage is concerned, IMO, the quicker you can get it to a rough bow shape, the quicker it'll dry and thus season faster. Good luck with yours.
I have built two bows from October '11 osage. I roughed them close to size and stuffed them under my bed for a 4-6 weeks. They are great bows, they dont follow the string at all and they zip a mean arrow. Both where heat formed and neither developed checks like wet wood often does with heat. That was mid-winter in Michigan, quite dry up here at that time. Storing blanks under your bed will dry them fast. Its the driest place in our home.
The back is sealed also. I took it to work and put it up in the rafters of my shop. About 20' up. It stays very warm up there.