Almost every renovation that runs late was optimistic on paper before it was late on site. The programme is usually the first thing a client is shown and the last thing anyone revisits honestly.
A useful programme has three things in it that an optimistic one does not: council approval time you do not control, a lead time for anything made to order, and a fortnight somewhere in the middle that belongs to nobody.
We would rather lose a job quoting sixteen weeks than win it quoting ten and spend the last six explaining ourselves. The number on the first page is a commitment, not a sales figure.