The Right Way to Set Expectations

You have likely been on both the asking and answering end of this question:

"How long will it take?"

If you are the one answering this question, more often than not the answer is more complicated than "2 days."  In those cases be very aware of how you frame your answer.  Most people will listen to what you tell them and only
pull out the portions that they need.  For instance, you may be thinking to answer in one of the following ways:

1) "If everything is set up it could take as little as one week."
2) "One month, but if everything is set up it may require less time."

Yes, there are variations of these statements, but the point is this....the people listening for the answer to "How long will it take?" are going to hear:

1) "blah blah blah blah one week."
2) "One month, blah blah blah blah."

If those are the ONLY data points they walk away with, what do you want them to think?  That they can do it in a week or a month?  If you subscribe to the idea of under-promise and over-deliver, I think you know the answer.  Though when the timelines are too far apart you risk not being asked to do the work at all, so be realistic.