Why always the rush?
Dumping a piece of green wood into a hot box is asking for troubles. Not just yew, but any wood. The outer surface will dry quickly, while the interior is still soaking wet. The outer wood cannot shrink, so it starts to check.
I´ve never used a hot box, but I don't really understand the hype about it. If you reduce the stave to near finished dimensions, you can work it today. Then just put it somewhere in the house to dry and it will dry in about 6 weeks or so. If you really cannot wait six weeks (maybe you're terminally ill), you can gently lay it in the hot box AFTER it has been drying for a week or two. This initial drying will drive out a lot of moisture, which makes it less likely that the wood will check. I can see a hot box being useful in lowering the MC from, say, 15% down to 8%, but not from green to 8%.