Most all the wood I make bows out of, I seal the ends with white glue or house paint, and set them off to the side (horizontally) for a minimum of a month before I attempt to work them into a bow.
I had good luck with a Hazel sapling about 2" in diameter once. Didn't bother sealing the ends, and started carving a bow out of it 3 weeks later. Left the bark on it, and tillered it more-or-less like an english longbow, with a rounded belly. Of course, it had a good crown on the back, since the bark was still intact.
As far as I know, the bow is still in use, at least 3 years later. It came out over 60 pounds at 26", and was about 74" in length.
Your mileage may differ.....
I've had other wood that I sealed and left for a year, and they split to unusable scrap an hour after I took the bark off.
Bow-building is as much art, as a science. I don't have experience with raw saplings of either oak or birch, so I can't help you there.....