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

Submitting this one as discussed with Bob so he can guide me further if any more changes need to be done.

I haven't formatted the text box with css. It's now showing class:fill-width property.

Waiting to know your review on this.

Had another pull request- but it was not getting "able to merge sign"- hence created a new branch and from it sending the pull request again.

We don't need to add this to the model as we don't need to store an extra piece of data. This should be a change to the form only, and when processing the form, if the `admin_time` form field is used then store that value in `execution_time`.