ship build time 1 turn?

Check out if there are weapons or other modules present.

If you just saved a design, but not the actual configuation, then want to make a new ship type out of it, but forget to further attach stuff you might get the pure hull, which could explain the short time.

Otherwise I dunno ...

You should probably fill out a ticket.

I'm not seeing this in the current game.  Can you submit a ticket with the save game attached so we can take a look?  Thank you.

https://esupport.stardock.com/index.php?/Tickets/Submit

i don't think so.  Do you know shipyard production rolls over? e.g. (simplistic example) if your yard is receiving 100 production per turn, and you build 10 ships at 50 cost, at the end of 10 turns you have built up  500 production points.  This would let you crank out 1 ship costing 500 pts in one turn. or 2 @250 over the next 2

i often use this in late game by pairing 1 Manufacturing world with several research/wealth worlds the research and wealth worlds "sponsor" a shipyard in the manufacturing worlds influence and then i simply rotate the manufacturing world to whichever shipyard has the least overflow production i can usually crank out 6 or more late game ships per turn from 1 manufacturing planet while still generating loads of overflow

Thanks for the answers. I will submit a ticket.  Its consistently one turn even for big ships, like colony ships in the early game, which should take a few turns.

open up the shipyard and hover over an empty space in the build que
it should show you overflow manufacturing 

If you're building CS in one turn during the first few turns of the games, you have to have some bug that no one else here has ever seen. I'd try starting a new game and making sure you're not using any mods.