Goal Setting Around Losing Weight by a Deadline

I recently read about a method for goal setting that intrigued me. It’s a formula: From x to y by deadline. So if I apply that to my desire to lose weight, it looks like: from 186 to 155 by December 31, 2017.

Is this a practical formula for weight loss? Or is it better to set a goal of creating a habit around my protocol? Such as setting a 90 day challenge to follow protocol every day for 90 days and not trying to control the results.

It would seem to me that I have greater control over my daily actions than I do over what exact results I achieve from those actions.