var now = new Date();

// Hier können die Grenzen von Tage und Nacht geändert werden:
var isDay = now.getHours() >= 7 && now.getHours() < 19;

function switchDayNight() {
  isDay = !isDay;
  setDayNightDisplayProperties();
}

function setDayNightDisplayProperties() {
  var dayDisplay = isDay ? "block" : "none";
  var nightDisplay = isDay ? "none" : "block";
  
  if (isDay) {
	  document.getElementById("h1_link").setAttribute("class", "h1_link");
	} else {
	  document.getElementById("h1_link").setAttribute("class", "h1_link_night");
	}
    
  document.getElementById("day_bg").style.display = dayDisplay;
  document.getElementById("day_logo").style.display = dayDisplay;
  document.getElementById("day_stage").style.display = dayDisplay;    
  
  document.getElementById("night_bg").style.display = nightDisplay;
  document.getElementById("night_logo").style.display = nightDisplay;
  document.getElementById("night_stage").style.display = nightDisplay;      
}