I learned early in my career to never give an executive a completion date or time estimate I hadn't thought long and hard about and had full confidence in. They

I learned early in my career to never give an executive a completion date or time estimate I hadn't thought long and hard about and had full confidence in. They won't remember any of the contingencies you tacked onto your estimate or the additional features they insisted on adding to the project after you talked, but they'll never forget when you said it would be done. It's far better to annoy them in the short term by saying what you'll need to provide an accurate time frame than it is to guestimate something that will bite you later.