Display hours on graph again (an JSHint track-view.js).

Hello,
I've tried JSHint on this file and it's a great tool. There is still one error but I'm not sure what to do with it: js/views/track-view.js: line 480, col 32, Use '===' to compare with '0'.
And I've tried to fix the hours display problem. It's working on my phone and I hope the date validation is correct ([picked up on StackOverflow](http://stackoverflow.com/questions/1353684/detecting-an-invalid-date-date-instance-in-javascript)).
I hope this could help.