I think the script is right here. But I have met test failed with reproduced rate 1/5. I guess the basic functionality of Pause/Resume is not working well. Because I'm able to reproduce it manually. Will file a bug for tracking it. We don't track the issue here.

'===== Log =====
1 passing (1 minutes)
  1 failing

  1) Timer Panel pausing and restarting:
      
      actual expected
      
      00:19:59
      
  AssertionError: Timer advances after being unpaused
      at Context.<anonymous> (/Users/ian/Documents/Dev/gaia/apps/clock/test/marionette/timer_panel_test.js:61:12)
      at Test.Runnable.run (/Users/ian/Documents/Dev/gaia/node_modules/mocha/lib/runnable.js:211:32)'