var d = new Date();
var h = d.getHours();

if (h < 3) greeting="Good early morning or late evening!";
else if (h < 7) greeting="Good early morning!";
else if (h < 12) greeting="Good morning!";
else if (h < 17) greeting="Good afternoon!";
else if (h < 23) greeting="Good evening!";
else greeting="Good late evening!";
document.write(greeting);