The ducks were 6 weeks old yesterday. The significance of that, is they have enough adult feathers grown in that they can be full time outside if we want them to be.
They are extra spazzy about dealing with the other birds, so I wasn't comfortable with just dumping them in the main bird yard and letting all the birds work it out (something we've done with previous young birds to reasonably good success - probably because of the large size of our bird yard). I was worried they'd freak out and run themselves into a fence (worst case, if they ran towards the neighbor border fence where the neighbor's dogs could possibly reach them) trying to get away from the scary larger birds.
M came up with a brilliant idea, and built me a small temporary yard situated between the mixed bird yard, and the goose yard. I strung up chicken wire along the neighbor border fence, so the neighbor's dogs shouldn't be able to reach them. I gave the ducklings the turtle water (an old plastic sandbox shaped like a turtle, that we turned into a pool many years ago) and a bucket for drinking water.
Yesterday they spent most of the daylight hours outside - but I still brought them in at night. I expect that by the beginning of next week, they'll be out 24/7, but I'm being overprotective for a short while longer.
ETA: I left the ducks out till after dark tonight and they made it very clear they do not like dark. They bunched up (M started calling them bunching ducks due to their tendency to cluster very close together when moving around or distressed) near a corner of their new outside yard and yelled about their displeasure. I could sit close to them, but they wouldn't budge towards the house till I picked them all up at once and moved them past the gate of their pen. They are now very contentedly sleeping in their inside "nest". I think I need to break out the extension cords and light I set up for the geese during their transition to being outside birds.