long getLastUpdateTime(ObjectName objectName) {
    ProxyInterface proxyInterface = findProxy(objectName, ProxyInterface.class);
    return proxyInterface.getLastRefreshedTime();
  }
This will return the last updated time of the proxyMBean

@param objectName {@link ObjectName} of the MBean
@return last updated time of the proxy
geode-core/src/main/java/org/apache/geode/management/internal/MBeanProxyFactory.java