Depending on the environment it has been subjected to, you could have cracking already, (I'm assuming he did not seal the ends and split onto staves for you).
I have taken Yew from standing to a bow in as little as a month, that is roughing out, sealing, and then using a hot box.
I don't recommend this because I have also ruined one or two by drying them too fast but I had plenty to play with and learn with.
I would treat it like most woods I wanted to minimize drying time on.........rough out a bow, seal the back and ends, I seal the whole bow when using the hot box. Put it on a caul of some sort the leave in a warm dry place. Depending on how warm and how dry, you could have it ready to work on in a month or two, considering that the Yew has been on the ground for seven months already. The stuff I was working with was fresh cut.
Mark