According to date/time field mapping table the 24 hours is valid: for a value of 24, the minute and second field must be zero per XML Schema Errata.

Therefore following test should print OK:

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;


class test {

    public static void main(String [] args) throws Exception {
        DatatypeFactory factory = null;
        try {
            factory = DatatypeFactory.newInstance();
        } catch (DatatypeConfigurationException dce) {
            dce.printStackTrace();
        }

        XMLGregorianCalendar calendar =
                factory.newXMLGregorianCalendar();
        calendar.setTime(24, 0, 0);
        System.out.println("OK");
    }
}

But it throws
Exception in thread "main" java.lang.IllegalArgumentException: Invalid value 24 for Hour field.
    at com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl.checkFieldValueConstraint(XMLGregorianCalendarImpl.java:1303)
    at com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl.setHour(XMLGregorianCalendarImpl.java:1310)
    at com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl.setTime(XMLGregorianCalendarImpl.java:1346)
    at com.sun.org.apache.xerces.internal.jaxp.datatype.XMLGregorianCalendarImpl.setTime(XMLGregorianCalendarImpl.java:1290)
    at pack.test.main(test.java:26)

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