Rather than timing the custom item via MediaLab, try adding this javascript to your custom item so that the continue/submit button will be disabled for whatever amount of time you like. In this sample script the button in the HTML form will be disabled for the first 10 seconds.
Code:
<script language="javaScript">
<!--
continue_at = "10000";
function continue_timer() { self.setTimeout("continue_enable();",continue_at); }
function continue_enable()
{
var submitObj = document.getElementById('continue_button');
submitObj.disabled = false;
}
//-->
</script>
<body onLoad="continue_timer();">
<form method="post">
<p>Your Answer: <input type="text" name="var" size="20"></p>
<p><input name="continue_button" type="submit" value="Continue" disabled></p>
</form>
</body>