[trikadin]

case true:
                            if(offset === 0) {
                                now = new Date();
                                offset = now.getTimezoneOffset() * 60000;
                            }
                            else {
                                return ;
                            }
                            break;
                        case false:
                            if(offset !== 0) {
                                clearTimeout(arguments.callee);
                                i = x - tm.getTime() + offset;
                                offset = 0;

А зачем case? if (arguments[0]) не?