document.observe('dom:loaded',function(){
	var currentTime = new Date()
  	var hours = currentTime.getHours()	

if(hours>=6&&hours<=20){
	$$("body")[0].style.backgroundImage="url(img_main/bg1.jpg)";
	
} else {
	$$("body")[0].style.backgroundImage="url(img_main/bg2.jpg)";
}
});