function isTime(curField, required, message){
	cField = curField.value;
	
	if(!required){
		if(cField.length == 0)
			return true;
	}	
	if(cField.length == 0){
		curField.focus();
		alert(message);
		return false;
	}	
	if(cField.length == 4){
		cField = "0" + cField;
	}
	colonLoc = cField.indexOf(":");
	if(!(colonLoc == 1 || colonLoc == 2 || cField.length == 4 || cField.length == 5)){
		curField.focus();
		alert(message);
		return false;
	} 
	
	hours = cField.substring(0,colonLoc);
	minutes = cField.substring(colonLoc + 1,cField.length + 1);
	if(!(hours.length == 2 && minutes.length == 2)){
		curField.focus();
		alert(message);
		return false;
	}
	for (i=0; i < hours.length; i++){
		if ((hours.charAt(i) < '0') || (hours.charAt(i) > '9')){
			curField.focus();
			alert(message);
			return false;
		}	
	}
	if(parseInt(hours) < 0 || parseInt(hours) > 23){
			curField.focus();
			alert(message);
			return false;	
	}
	for (i=0; i < minutes.length; i++){
		if ((minutes.charAt(i) < '0') || (minutes.charAt(i) > '9')){
			curField.focus();
			alert(message);
			return false;
		}	
	}
	if(parseInt(minutes) < 0 || parseInt(minutes) > 59){
			curField.focus();
			alert(message);
			return false;	
	}
	curField.value = cField;
	return true;

}