gistfile1.txt

// ==UserScript==
// @name           Ichigo-Mashimaro
// @namespace      http://kentarok.org/
// @include        http://twitter.com/*
// ==/UserScript==

(function () {
    var textarea = document.getElementById('status');
        textarea.value = '';
    var start = null;
    textarea.addEventListener(
        'keyup',
        function (event) {
            if (!start) start = (new Date);
            if (event.target.value == '@kentaro しごとしろ') {
                var time = (new Date) - start;
                event.target.value = event.target.value + ' (' + time / 1000 + '秒)';
            }
        },
        true
    );
})();