Local Date

function equalsDate(a, b) {
    return (a.getDate() === b.getDate() &&
            a.getMonth() === b.getMonth() &&
            a.getFullYear() === b.getFullYear());
}

var today = new Date();
var yesterday = new Date();
yesterday.setDate(yesterday.getDate()-1);
var dateList = document.getElementsByTagName('time');
var optionsDate = {
    year: "numeric",
    month: "short",
    day: "numeric",
};
var optionsTime = {
    hour: "2-digit",
    minute: "2-digit",
};
for (i = 0; i < dateList.length; i++) {
    var text = dateList[i].innerHTML;
    var datum = new Date(text);
    dateList[i].innerHTML = (equalsDate(datum, today) ? "dnes " :
            (equalsDate(datum, yesterday) ? "včera " :
             (datum.toLocaleString(undefined, optionsDate) + " "))) +
        datum.toLocaleString(undefined, optionsTime) + " &ndash;";
    dateList[i].title = text;
}