function getCSS()
{
datetoday = new Date();
timenow=datetoday.getTime();
datetoday.setTime(timenow);
thehour = datetoday.getHours();

if (thehour > 18)
display = "night.css";
else if (thehour > 6)
display = "day.css";
else
display = "day.css";

var css = '<'; css+='link rel="stylesheet" href=' + display + ' \/'; css+='>';

document.write(css);
}
getCSS();