var d = new Date()
var time = d.getHours()

if (time > 4 && time <= 10) 
{
document.write("Guten Morgen!")
}
if (time > 10 && time <= 18) 
{
document.write("Guten Tag!")
}
if (time > 18 && time <= 23) 
{
document.write("Guten Abend!")
}
if (time == 0 || time <= 4) 
{
document.write("Gute Nacht! So sp&auml;t noch auf!?")
}