if(command == "what time is it")
{
    var now = System.DateTime.Now;
    await GUIOutput("It's " + now.Hour.ToString("D2") + ":" + now.Minute.ToString("D2"), true);
    state = AssistantState.BACKGROUND_DEFAULT;
}

This piece of code takes the current time of the system and uses it to create the output string to be passed to the GUIOutput function. Such a function is the one that handles the visual and audio output: it uses the code snippet for the interaction between application and UI threads and the function SayAsync (see here and here for more details).