Alexodiy,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
window.addEventListener('DOMContentLoaded', function() {
var select = document.querySelector('[name="sitetime"]'),
res = document.getElementById('rez');
select.addEventListener('change', function() {
res.value+=this.value+','
});
});
</script>
</head>
<body>
<select name="sitetime" id="sitetime" >
<option value="" ></option>
<option value="1" >60</option>
<option value="2" >90</option>
<option value="2" >120</option>
<option value="3" >150</option>
<option value="3" >180</option>
<option value="4" >210</option>
<option value="4" >240</option>
<option value="5" >270</option>
<option value="5" >300</option>
</select>
<input type='text' id='rez' />
</body>
</html>