I have heard people use 1 inch per year as a rough guide to seasoning. So, if you have a one inch thick plank, it is seasoned in 6 months, a 12 inch diameter log, in about 6 years. Obviously that will depend on how it was kept, and on the wood (some species are slower to dry than others).
For bows, you could either make short ones, or make billets and finger splice them at the handle. I haven't ever used the stuff, so don't know what its properties would be, or whether it would make a good handle. There should be information on the Net about it. Its suitability for knife handles has more to do with how it looks, its density, hardness and how porus it is, rather than its ease of carving or how tough it is. Oak is tough, but isn't all that popular as a handle.
You could try cutting off a 6inch length and reducing it into handle blocks for knives to get an idea of what it looks like, then you would still have enough to use as bow billets if you wanted to give that a try. Just a thought.