They do have a penalty of 50$ per day over their allocated build time with 10 days allowable for weather.
There is absolutely nothing unrealistic about a 16 day build plus a very generous weather allowance of 10 days.
In fact, I think that I know who your builder is!
https://www.youtube.com/watch?v=rwvmru5JmXk
haha well spotted, my secret is out.