This is a great question. The short & sweet answer; 20 to 40%
Here is the 'big picture'. Cue makers go to great lengths to acclimate and stabilize their woods to THEIR environment. We let them hang for years. Even though the wood may be kiln-dried before we get it, the wood needs to 'get used to' it's new home in our shops. Some of the exotics that we use are not kiln-dried and are coated in wax to assure that the wood doesn't dry too quickly and start 'checking'. Checking (surface cracks) is the result of the wood drying too quickly on the surface, faster than what it's drying at it's core. As wood drys, it can go through dimensional changes. It can twist, bow, shrink and build-up internal stress. If you've ever heard of a cue maker cutting his wood in stages over a lengthy period of time, it's in an effort to hasten the drying process and to eliminate the stresses that would be building in the wood if it were to just sit and dry over time.
I buy most all of my birdseye maple from the upper peninsula of Michigan, The Birdseye Capital of The World. I'm always amazed at the fact that the wood comes out of the kiln at 6 to 8% moisture yet by the time it reaches me, it can be up to 12 to 14%. Then, after sitting in my shop for a while, it can be up to 16 to 18%. What's happening is that the wood is reclaiming moisture. Wood will acclimate itself to it's environment. My shop is within 100 yds of a rather large lake so I expect this.
One thing that has always concerned me is, where that cue is going once it's built and sold. If the cue's new home is an environment that is considerably drier (or wetter) that the environment in which the cue was built, there is the risk that the cue will 'move'. Sometimes this movement can be temporary and sometimes it can be permanent. It's all up to the wood. Wood seems to have a mind of it's own and it's not always rational or logical. It's just the nature of the beast.
This was probably WAY more than you wanted to know but when I address a question, sometimes it's not enough to just give the answer. There are times when the reasoning as to WHY that's the answer can lead to a better understanding. I hope this helps. KJ