JQuery :: SetTimeOut Before Form Submit

I have a form and I'd like to change a background image when the form is ready to be submitted but wait for a few seconds before it can redirect to the action page. In order to do that I have used the setTimeOut function but it doesn't seem to care. If I integrate the preventDefault method the form doesn't submit in the end...
$('document').ready(function() {
$('#submit').click(function(event) {
var error = 0;
$('#key_form input').each(function(element){
if($.trim($(this).val()) == "") {
error = error + 1;
}});
if(error) {
event.preventDefault();
$("div.warning").text("Please insert your activation key").css("border", "1px solid #F00");
return false;
} else {
$("div.warning").removeAttr("style").empty();
$('#step0').css({"background" : "#FFF url(images/unlocked.png) top right no-repeat"});
setTimeout(function() {
$('#key_form').submit();
},8000);}
//event.preventDefault();
});});
How can I accomplish that?