Hey Big George:
We've had some cut for several days before we got it sunk but we put the butt ends in the water so it didn't dry out too much. I don't think it would hurt the bamboo to dry out some but it may make it more difficult to sink. It is very buoyant even when fresh cut so if you let it dry out too much you'll have to make sure you have plenty of weight to sink it.
The few times we've had trouble getting our bamboo condos to sink was when we used some that had too large of diameter stalks and left them too long. Since the stalks are hollow and sealed between the "knuckles" the bigger diameter they are and the longer they are then the more buoyancy they provide.
As long as we use boo that is no more than about 1 1/4-inch in diameter we don't have any problem. We'll use a few larger ones if they have a real good "bushy top" to "butt end diameter" ratio but we cut more of the stalk off to reduce buoyancy.
We plan on demonstrating how to build and sink both the tall “Bucket/QuickCrete” and the “Cement Block” type at Crappie Camp for anyone that is interested. Come join us!