As discussed on the mailing list in relation to
LOG4J2-1883, there’s a consensus that additional time related classes should not be added to the core.util package. Additionally, the Log4j community wants to start clarifying which classes are published and which classes are internal to Log4j2.
The classes in the util.datetime package, although public, were never intended to be used directly by client code outside of Log4j. The hope is that the new package name clarifies the intended usage better.