var months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Ago', 'Sep', 'Oct', 'Nov', 'Dec'];
var base = 1510080000;
var delta = 1210000;
var span;

function formatDate(d) {
    return d.getDate() + " " + months[d.getMonth()] + ' ' + d.getFullYear();
}

function diff(d) {
    d = Math.floor(d);
    if (d > 172800) {
        return Math.floor(d / 86400) + ' days'
    } else if (d > 7200) {
        return Math.floor(d / 3600) + ' hours'
    } else if (d > 120) {
        return Math.floor(d / 60) + ' minutes'
    } else {
        return d + ' seconds'
    }
}

function setup() {
    var coll = document.getElementsByTagName('table')[1].rows[0].cells;
    var dObj = coll[coll.length - 1].children[0];
    dObj.innerHTML += ' <span style="color:#e00000;font-size:80%;font-weight:bold" id="sp_btt_ext"></span>';
    span = document.getElementById('sp_btt_ext');
}

function main() {
    var elapsed = new Date() / 1000;
    var previous = Math.floor((elapsed - base) / delta) * delta + base;
    var next = previous + delta;
    var perc = (elapsed - previous) / delta;
    var dPrev = new Date(previous * 1000);
    var dNext = new Date(next * 1000);
    span.title = 'Current period started ' + formatDate(dPrev) + ' (' + diff(elapsed - previous) + ' ago)\nNext period starts ' + formatDate(dNext) + ' (in ' + diff(next - elapsed) + ')';
    span.innerHTML = (perc * 100)
        .toFixed(2) + '%';
}
setup();
main();
window.setInterval(main, 1000);