Well I looked here everything is correct, it works correctly your code tested in the newest Chorme and in the IE 11, maybe the rest of the codes of your page is interfering. But I have reservations for your code that would be:
1) I believe that the CSS property that 'hides' your DIV should be in the element itself, I say this because depending on the running time of the browser, until you start loading the JS the content may appear, and being in the element itself the chance of this occurring is minimal. Then it would look like this:
<div id="mame" style="display: none;">CONTEUDO</div>
2) Depending on how much content there is on your page outside that code may or may not be the content of the DIV shown in the correct time, so I would check if all the content was executed and after that triggered the event of 10 seconds.
Adding these two observations together your code would look like this:
<div id="mame" style="display: none;">CONTEUDO</div>
<script>
window.onload = function() { // Espera tudo ser carregado para executar
var div = document.getElementById("mame"); // Pega o objeto do elemento DIV
window.setTimeout(function() { // Inicia a contagem de 10 segundos
div.style.display = ""; // Remove a proriedade que esta escondendo a DIV
}, (10 * 1000));
}
</script>
You can explain better "and open along with my div"?
– Sergio