var thedate   = new Date();
var dayofweek = thedate.getUTCDay();
var hourofday = thedate.getUTCHours();

function onAir()
{
   // return TRUE if it's Mon through Sat, 3a-6a UTC

   if (dayofweek != 0 && 
      ((hourofday > 3 && hourofday < 19))) {
     return true;
   }
   return false;
}