If your manager asks for a "rough time estimate" for a project, there is a higher than 99% chance that your answer will be written down and be used in presentations of project roadmap to upper management and/or marketing, who will create a hard deadline based on your rough estimate and communicate this to customers/clients, and then blame you for not keeping the deadline when it turns out (as it always does) that the rough estimate was off by several months because feature creep caused by upper management.