Your calendar does not include weekends as working time -- other than setting Sunday, January 1 as a working day. Duration in project is Monday through Friday by default (working days) and I'm a bit confused by your statement:

"I want the dates to include the weekends. However noone works on the weekends."

There are 40 working days between Jan 1 and Feb 23. I have no idea what you mean by "adding up to 54 instead of 56." The tasks "Product Rationale" and "Product Specification" are running at the same time therefore the longest duration showing at the summary line is 40 days.



If you want to count all calendar days, alter your project calendar (Project > Change Working Time) to include Saturday and Sunday as working days.