Bug 1036928 - Allow to set longer time estimages as 60 minutes

Closed the previous pull- working only on this branch now.
I see you re-added this. I know that removes the error message you were seeing, but it isn't the solution. As I mentioned before, we do not want this field on the model.

You need to create a new field for the form, in `forms.py`. The key is that you need to create a form field that is not bound to a model field. Take a look at https://docs.djangoproject.com/en/1.4/topics/forms/ for more info on how django forms work.