Try entering this in your postbit where you want it to show up. Chance the field5 to whatever your custom profile field # is. You may want to go into phpmyadmin and change the field type to one of the date formats.
PHP Code:
<if condition="$post[field5]">
<div>
<Script language='Javascript'>
var rndNum = Math.floor(Math.random() * 10000);
var tempString="$post[field5]";
tempArray=explodeArray(tempString,";");
document.writeln("<form name='form" + rndNum + "' action='javascript:void(0);'>");
document.writeln('<font size=2 color="'+tempArray[2]+'">
IF YOU WANT TEXT ENTER IT HERE
</font><BR>');
document.writeln("<input type=text value='' size=40 name='countdown'>");
document.writeln("</form>");
countdown(tempArray[0], rndNum, tempArray[1]);
</script>
</div>
</if>