Here you go, with a built in alert at 30 minutes:

javascript:(function(){window.status.length||(window.setTimeout(function(){alert("Go vote on "+document.title+"!")},1000*60*(30-parseInt(document.getElementsByTagName("time")[0].innerHTML))),window.status="",setInterval(function(){document.getElementsByClassName("Post").length?(window.status.length||(window.status=document.title),document.title="["+document.getElementsByTagName("time")[0].innerHTML+"] - "+window.status):window.status=""},500));})();

The unminified code:

javascript: (function() {
    if (!window.status.length) {
        window.setTimeout(function() {
            alert("Go vote on " + document.title + "!");
        }, 1000 * 60 * (30 - parseInt(document.getElementsByTagName("time")[0].innerHTML)));
        window.status = "";
        setInterval(function() {
            if (document.getElementsByClassName("Post").length) {
                if (!window.status.length) window.status = document.title;
                document.title = "[" + document.getElementsByTagName("time")[0].innerHTML + "] - " + window.status;
            } else window.status = "";
        }, 500);
    }
})();

If you want to get in earlier than 30 minutes, just change the 30 in there to something else like 28, 25, etc.