Ok, after going back and starting a new game, and looking closer at the two screens...

In the above screen, the selected ship's parenthetical notation exactly matches the weeks remaining. I went through the list, and they all matched.

In the shipyard, the notation matches the number of ships in each class.
Had me all
because I see the shipyard screen way more often than I see the build-at-this-planet screen. Usually I use the quick build list -- an excellet feature, btw.