Just like with the vast majority of project forecasts the "few days" is what you say to get the sale - internally or to outside clients. If you think it is that

Just like with the vast majority of project forecasts the "few days" is what you say to get the sale - internally or to outside clients. If you think it is that simple, well, I would like to sell you just a few days of machine learning expertise if you have a project... :) Even very simple tasks that you can let the intern do can - and often does - take days longer than projected.