I don’t think Wikileaks is choosing their timing. They are not, and have never claimed to be, a journalistic outfit: if they were, they would assert control over their material and choose particular material to release (which they do not).
They are a repository for leaked material. The value of the leaked material is occasionally useful as a PR strategy to get more support, but they have no particular problem hosting uninteresting leaks — which is most of what they supply.
Don’t compare them to the New York Times; instead, compare them to MegaUpload.