Hi Jitender,
I just tried, driver.getDeviceTime() on iOS Simulator and android device and it's working. My driver object is Android / IOSDriver object
Android
AppiumDriver driver = new AndroidDriver(service.getURL(), capabilities);
driver.getDeviceTime();
iOS
AppiumDriver driver = new IOSDriver(service.getURL(), capabilities);
driver.getDeviceTime();
Could you please tell about your driver object?