var axu_urlday="../work/css/day.css"; 
var axu_urlnight="../work/css/night.css";
datetoday = new Date();
timenow=datetoday.getTime();
datetoday.setTime(timenow);
thehour = datetoday.getHours();
if(thehour<6)
document.getElementById("skin").href=axu_urlnight;  

else if (thehour>17)
document.getElementById("skin").href=axu_urlnight; 

else document.getElementById("skin").href=axu_urlday;