下記のコードは、誕生日が来たらメッセージが表示され、誕生日が過ぎたら次の誕生日まで
デジタル時計が表示されるように設定されています。
これを、誕生日が来たら１分ごとにメッセージをa)とb)に切り替えるようにするには、
どうすればいいでしょうか。
偶数の分(〇%2==０)と奇数の分(〇%２==０+1)をうまく入れられません。

a) 偶数の分のメッセージ: 金さん銀さん 〇歳の誕生日おめでとう！！！！！
b) 奇数の分のメッセージ: 後で、プレゼントを送ります☆

<!DOCTYPE html>
<html lang="ja">
<head>
<meta http-equiv="Content-type" content="text/html; charset=Shift_JIS">
<meta http-equiv="Content-Script-Type" content="text/javascript">
<meta http-equiv="Content-Style-Type" content="text/css">
<title></title>


<style type="text/css">

/* Circle Text Styles */
#myText {
font-style: italic;
font-weight: bold;
font-family: 'comic sans ms', verdana, arial;
color: gold;

position: absolute;top: 0;left: 0;z-index: 3000;cursor: default;}
#myText div {position: relative;}
#myText div div {position: absolute;top: 0;left: 0;text-align: center;}
/* End Required */
/* End Circle Text Styles */
</style>

<script type="text/javascript">
<!--

;(function(){

var birthday = new Date(1917, 3, 8);
var isBirthDay = false;

if((new Date().getMonth() == birthday.getMonth()) && (new Date().getDate() == birthday.getDate())) {
    var age = new Date().getYear()- birthday.getYear();
    var msg="金さん銀さん"+" "+age+"歳"+"の誕生日"+" "+"おめでとう！！！！！";
    isBirthDay = true;

} else {
  var ti = new Date;

     var Hour = ti.getHours();
     var Min = ti.getMinutes();
     var Sec = ti.getSeconds();

        if(Hour <= 9) { 
                       Hour = "\u0020\u0020" + Hour; 
}        
　　　　if(Min <= 9) { 
                       Min = "0" + Min; 
}
        if(Sec <= 9) { 
                       Sec =  "0" +  Sec; 
}

var msg = Hour + ":" + Min + ":" + Sec ;
}

var size = 24;

var circleY = 0.75; var circleX = 2;

var letter_spacing = 5;

var diameter = 10;

var rotation = 0.4;
var speed = 0.3;


if (!window.addEventListener && !window.attachEvent || !document.createElement) return;

msg = msg.split('');
var n = msg.length - 1, a = Math.round(size * diameter * 0.208333), currStep = 20,
ymouse = a * circleY + 20, xmouse = a * circleX + 20, y = [], x = [], Y = [], X = [],
o = document.createElement('div'), oi = document.createElement('div'),
b = document.compatMode && document.compatMode != "BackCompat"? document.documentElement : document.body,

mouse = function(e){
 e = e || window.event;
 ymouse = !isNaN(e.pageY)? e.pageY : e.clientY; // y-position
 xmouse = !isNaN(e.pageX)? e.pageX : e.clientX; // x-position
},

makecircle = function(){ // rotation/positioning
 if(init.nopy){
  o.style.top = (b || document.body).scrollTop + 'px';
  o.style.left = (b || document.body).scrollLeft + 'px';
 };
 currStep -= rotation;
 for (var d, i = n; i > -1; --i){ // makes the circle
  d = document.getElementById('iemsg' + i).style;
  d.top = Math.round(y[i] + a * Math.sin((currStep + i) / letter_spacing) * circleY - 15) + 'px';
  d.left = Math.round(x[i] + a * Math.cos((currStep + i) / letter_spacing) * circleX) + 'px';
 };
},

drag = function(){ // makes the resistance

var birthday = new Date(1917, 3, 8);
var isBirthDay = false;

if((new Date().getMonth() == birthday.getMonth()) && (new Date().getDate() == birthday.getDate())) {
    var age = new Date().getYear()- birthday.getYear();
    var msg="金さん銀さん"+" "+age+"歳"+"の誕生日"+" "+"おめでとう！！！！！";
    isBirthDay = true;

} else {

  var ti = new Date;

     var Hour = ti.getHours();
     var Min = ti.getMinutes();
     var Sec = ti.getSeconds();

        if(Hour <= 9) { 
                       Hour = "\u0020\u0020" + Hour; 
}        
　　　　if(Min <= 9) { 
                       Min = "0" + Min; 
}
        if(Sec <= 9) { 
                       Sec =  "0" +  Sec; 
}

var msg = Hour + ":" + Min + ":" + Sec ;
}

msg = msg.split('');
var n = msg.length - 1;
for (var d, i = n; i > -1; --i)
{
    var elm = document.getElementById('iemsg' + i);
    elm.innerHTML = msg[i];
};

 y[0] = Y[0] += (ymouse - Y[0]) * speed;
 x[0] = X[0] += (xmouse - 20 - X[0]) * speed;
 for (var i = n; i > 0; --i){
  y[i] = Y[i] += (y[i-1] - Y[i]) * speed;
  x[i] = X[i] += (x[i-1] - X[i]) * speed;
 };
 makecircle();
},

init = function(){ // appends message divs, & sets initial values for positioning arrays
 if(!isNaN(window.pageYOffset)){
  ymouse += window.pageYOffset;
  xmouse += window.pageXOffset;
 } else init.nopy = true;
 for (var d, i = n; i > -1; --i){
  d = document.createElement('div'); d.id = 'iemsg' + i;
  d.style.height = d.style.width = a + 'px';
  d.appendChild(document.createTextNode(msg[i]));
  oi.appendChild(d); y[i] = x[i] = Y[i] = X[i] = 0;
 };
 o.appendChild(oi); document.body.appendChild(o);
 setInterval(drag, 25);
},

ascroll = function(){
 ymouse += window.pageYOffset;
 xmouse += window.pageXOffset;
 window.removeEventListener('scroll', ascroll, false);
};

o.id = 'myText'; o.style.fontSize = size + 'px';

if (window.addEventListener){
 window.addEventListener('load', init, false);
 document.addEventListener('mouseover', mouse, false);
 document.addEventListener('mousemove', mouse, false);
  if (/Apple/.test(navigator.vendor))
   window.addEventListener('scroll', ascroll, false);
}
else if (window.attachEvent){
 window.attachEvent('onload', init);
 document.attachEvent('onmousemove', mouse);
};

})();

// -->
</script>

</head>

<body bgcolor="black">

</body>
</html>

追記)以下のコードできちんと分離されるはずですが、elseの表示(奇数の分の場合)のとき、
　　　　ifの表示と合併されて表示されます。理由が分かる方は、教えていただけませんか。

～中略～
var birthday = new Date(1917, 3, 8);
var isBirthDay = false;

if((new Date().getMonth() == birthday.getMonth()) && (new Date().getDate() == birthday.getDate())){

var date = new Date;
var minutes = date.getMinutes();
 var   isBirthDay = true;

  if(minutes%2==0){

    var age = new Date().getYear()- birthday.getYear();
    var msg="金さん銀さん"+" "+age+"歳"+"の誕生日"+" "+"おめでとう！！！！！"+" ";

} else {

  var ti = new Date;

     var Hour = ti.getHours();
     var Min = ti.getMinutes();
     var Sec = ti.getSeconds();

        if(Hour <= 9) { 
                       Hour = "\u0020\u0020" + Hour; 
}        
　　　　if(Min <= 9) { 
                       Min = "0" + Min; 
}
        if(Sec <= 9) { 
                       Sec =  "0" +  Sec; 
}

var msg = Hour + ":" + Min + ":" + Sec ;

}
}
～中略～