You still have three and a half months to get that yew dry then. That should be enough, even without really quick drying. How quick should drying wood be to still qualify as quick drying? I dunno. But three months isn't quick drying in my book.
Rough the stave out somewhat. Not even CLOSE to bow shape, but just remove the bulk to make it THINNER, not narrower. Store indoors at, or slightly below, room temperature with a RH of 50-60% for two months. Then reduce to floor tillered dimensions and store the blank again at room temperature and RH 40-50% for one more month. Then continue making a bow, until you are halfway in the tillering process. Then put it aside again for two more weeks at room temp. and perhaps a slightly lower RH of around 40%. The wood should be dry by then, although some people might argue it won't exactly be seasoned/aged.
I strongly dislike speed/quick drying wood. Especially yew, which is so rare and precious. But if that wood needs to be dry in July, I think three and a half months should be enough to get you there, if you time the steps right and keep an eye on the wood. It should be enough time to get you there, but it's tricky. Possibly not worth the risk, but it's doable.