It took Sun about a year to publish all of the JDK code they could under the GPL (~96 %), and
another year together with the OpenJDK community to finish off the remaining bits needed to
certify an implementation as Java6 compatibile.
The only comparison that remotely makes sense that I know of is the tri-licensing of the
Mozilla code base, which took 5 years until completion, afaik.
Two years from 0 to 100% is quite the opposite of slow for a radical licensing change on
codebase as mature and large as Java.