After digging away fruitlessly for what seems like an eternity, Tom and Huck finally seem to have realized why they still haven't found any buried treasure: it's all in the timing. Digging during the daylight hours is a waste of time, because according to Tom, you have to dig in the shadow of the tree's limb at midnight. Whether we can accept that Tom knows what he's talking about is a moot point. After all, he just told Huck that maybe witches were putting the hex on them even though, as Huck points out, witches don't have any power during the day time.
But even when they come back at midnight, they still can't find the treasure. And once again, it's the timing that's the problem. The boys are either too late or too early; they can never be there at just the right time. To make matters worse, Huck reckons there are lots of ghosts and witches lurking around, and it's really creeping him out.