How to sort date in n-day/week/month/year format?

I have a table that displays the 'freshness' of posts in this format:

30 second,
1 week
3 day,
5 month

But I can't figure out how to sort them, this is what I've achieved so far:

function getRank(name) {

    //newname = name.slice(2,name.length);
    //alert(name);
    newname = name;
    var rankNumber;

    if (newname == "1 day"){
        rankNumber = 1;
    } else if (newname == "week"){
        rankNumber = 2;
    } else if (newname == "month") {
        rankNumber = 3;
    } else if (newname == "year") {
        rankNumber = 4;
    }
    console.log(newname);
    return rankNumber + parseInt(name.slice(0,1));

}

jQuery.fn.dataTableExt.oSort["rank-desc"] = function (x, y) {

    return getRank(x) < getRank(y);

};

jQuery.fn.dataTableExt.oSort["rank-asc"] = function (x, y) {
return getRank(x) > getRank(y);
}

$(document).ready(function () {
var oTable = $('#topics').dataTable({
"autoWidth": false,
"bLengthChange": false,
"fixedColumns": true,
"aoColumnDefs" : [{
"bSortable" : true,
"aTargets" : [5],
"sType": "rank"
}]
});