today = new Date();

if ((today.getHours() >= 6) && (today.getHours() <= 12))
{
   document.write("Good morning and ");
}

if ((today.getHours() > 12) && (today.getHours() <= 18)) 
{
   document.write("Good afternoon and ");
}

if ((today.getHours() > 18) && (today.getHours() < 24)) 
{
   document.write("Good evening and ");
}

if ((today.getHours() >= 0) && (today.getHours() < 3)) 
{
   document.write("Wow, are YOU up late!  Anyway, ");
}

if ((today.getHours() >= 3) && (today.getHours() < 6)) 
{
   document.write("Wow, are YOU up early!  Anyway, ");
}