It can be done at just about any time, and smaller seedlings transplant much easier than more established ones. The stemmed hellebores, including foetidus, argutifolius, and lividus, are all somewhat touchy about transplanting, so be careful to get as many roots as possible and to avoid touching the stem, if at all possible - it's best to handle the plant by one of its leaves when moving it. If you're potting them up, drainage is crucial; I add lots of perlite, grit, etc., to the potting mix, especially for this species.

I know i transplant my babies of orientalis or hybridus, whichever you prefer, in spring after a soaking rain. I work an old paring knife down in the soil to loosen it and gently tug them out and replant them in pots or the garden asap. They do hold a day or so in a slightly moist washcloth. It's much easier to get the first season seedlings than ones i missed the year prior out safely and healthy. Since they germinate now, i guess it would work to move them now. There tend to be a whole lot of them- more than it looks- so, why don't you do half now and half later? By the time you get through 1/2 you'll want the break anyhow. Then you can decide which seedlings did better and go with that method from then on. I only have a couple foetidis, and haven't had seedlings thus far so i don't know specifically about them.