Deron Williams does not become eligible for a contract extension until July, which is the three-year anniversary of his previous extension from July 18th, 2008.
Dwight Howard is also a potential member of the 2012 free agency class and is eligible to sign an extension now because he signed his in 2007. Howard first became eligible to sign an extension on July 12, 2010.
Chris Paul signed his previous extension on July 9, 2008, so he must also wait until July to sign an extension.
Williams and Paul must also wait until a new collective bargaining agreement is complete before an extension can be reached.