Keep new session when refresh page in nodejs

i have got 0.8.21 nodejs and 3.1.0 express framework (modules are latest). there is famous heroku project with express, mongodb and passport auth:

https://github.com/madhums/nodejs-express-mongoose-demo

Session storage:

  var express = require('express')
    , mongoStore = require('connect-mongo')(express)

  ...

  app.use(express.logger('dev'))

  // set views path, template engine and default layout
  app.set('views', config.root + '/app/views')
  app.set('view engine', 'jade')

  app.configure(function () {
    // dynamic helpers
    app.use(viewHelpers(config))

    // cookieParser should be above session
    app.use(express.cookieParser())

    // bodyParser should be above methodOverride
    app.use(express.bodyParser())
    app.use(express.methodOverride())

    // express/mongo session storage
    app.use(express.session({
      secret: 'noobjs',
      store: new mongoStore({
        url: config.db,
        collection : 'sessions'
      })
    }))

    // connect flash for flash messages
    app.use(flash())

    // use passport session
    app.use(passport.initialize())
    app.use(passport.session())

    app.use(express.favicon())

    // routes should be at the last
    app.use(app.router)

    ...

QUESTION: I want users to log in only for 70 seconds, so i wrote cookie: {maxAge: 70*1000}, after app.use(express.session({ and what happens: users can walk via site only 70 seconds, than they are logged out. IF user refresh page or go over link, session UPDATED to database like:

{ "_id" : "cVYWfv7kHbaEPNUCD2Bbbaw4",
  "session" : "{\"cookie\":{\"originalMaxAge\":70000,\"expires\":\"2013-03-02T14:46:52.146Z\",\"httpOnly\":true,\"path\":\"/\"},\"passport\":{\"user\":\"51320f3fd04c162d14000003\"},\"flash\":{}}",
  "expires" : Date( 1362235612146 ) }

BUT ANYWAY USER IS LOGGED ON ONLY 70 SECONDS. I mean that session updates to mongodb, new expires date, BUT user STILL CAN BE LOGGED ON only 70 second SINCE LOG IN.

Help me, please. Thank you.