create an ISODate for mongo queries, usage aDate : { $gt:queryDate({hour:-4}), $lt:queryDate() }

mongoQueryDate.js

var queryDate = function (diff) {
    var d = new Date(), p = function(num){return num<10?"0"+num:num+"";};
    diff = diff || {};
    d.setUTCFullYear(d.getUTCFullYear() + (diff.year||0));
    d.setUTCMonth(d.getUTCMonth() + (diff.month||0));
    d.setUTCDate(d.getUTCDate() + (diff.day||0));
    d.setUTCHours(d.getUTCHours() + (diff.hour||0));
    d.setUTCMinutes(d.getUTCMinutes() + (diff.min||0));
    return ISODate(d.getUTCFullYear() + "-" +
                p(d.getUTCMonth()+1) + "-" +
                p(d.getUTCDate()) + "T" +
                p(d.getUTCHours()) + ":" +
                p(d.getUTCMinutes()) + ":00.000Z");
};