Ojo si funciona:

<font size="2"><script language="JavaScript" type="text/javascript">
//<![CDATA[
<!--
today = new Date()
if(today.getMinutes() < 10){
pad = "0"}
else
pad = "";
document.write ;if((today.getHours() >=6) && (today.getHours() <=9)){
document.write("¡Buen día!")
}
if((today.getHours() >=10) && (today.getHours() <=11)){
document.write("¡Buen día!")
}
if((today.getHours() >=12) && (today.getHours() <=19)){
document.write("¡Buenas tardes!")
}
if((today.getHours() >=20) && (today.getHours() <=23)){
document.write("¡Buenas noches!")
}
if((today.getHours() >=0) && (today.getHours() <=3)){
document.write("¡Buenas noches!")
}
if((today.getHours() >=4) && (today.getHours() <=5)){
document.write("¡Buenas noches!")
}
// -->
//]]>
</script></font>