slow findOne query performance

Performance of individual findOne query is abnormally slow (upwards of 60-85ms). Is there something fundamentally wrong with the design below? What steps should I take to make this operation faster?

Goal (fast count of items within a range, under 10-20ms):

• Input max and min time
• Query database for document with closest time for max and min
• Return the "number" field of both query result
• Take the difference of the "number" field to get document count

Setup

MongoDB database

3000 documents, compound ascending index on time_axis, latency_axis, number field

[   {   time_axis:1397888153982,latency_axis:5679,number:1},    
    {   time_axis:1397888156339,latency_axis:89 ,number:2}, 

                ...     
    {   time_axis:1398036817121,latency_axis:122407,number:2999},   
    {   time_axis:1398036817122,latency_axis:7149560,number:3000}   ]

NodeJs

exports.getCount = function (uri, collection_name, min, max, callback) {
    var low, high;
    var start = now();
    MongoClient.connect(uri, function(err, db) {
        if(err) {
            return callback(err, null);
        }
        var collection = db.collection(collection_name);
        async.parallel([
            function findLow(callback){
                var query = {time_axis : { $gte : min}};
                var projection = { _id: 0, number: 1};
                collection.findOne( query, projection, function(err, result) {
                    low = result.number;
                    console.log("min query time: "+(now()-start));
                    callback();
                });
            },
            function findHigh(callback){
                var query = {time_axis : { $gte : max}};
                var projection = { _id: 0, number: 1};
                collection.findOne( query, projection, function(err, result) {
                    high = result.number;
                    console.log("max query time: "+(now()-start));
                    callback();
                });
            }
        ], 
        function calculateCount ( err ){ 
            var count = high - low;
            db.close();
            console.log("total query time: "+(now()-start));
            callback(null, count);
        });
    });
}

Note: Thank you for Adio for the answer. It turns out mongodb connection only need to be initialized once and handles connection pooling automatically. :)