I would leave them in their pots, as they are. Helleborus prefer a well drained, neutral to slightly alkaline soil and the soil mix in your pot has likely been conditioned for them. You could place the pot inside a decorative pot, for appearances, if you wish.
When preparing the soil for planting, drainage is important,
as you noted. Select a location with some morning sun, dappled sun/shade or bright shade. They do not bloom well. if at all, in deep, evergreen shade.
Mix a generous amount of compost, ground composted coniferous bark and coarse washed sand or grit with the clay to promote drainage. Do not use fine or play sand alone to amend clay, as you could wind up with adobe brick! I usually incorporate about one cup of Dolomitic Lime into the mix to raise the soil pH.
You could also use crushed concrete or sea shells to provide Calcium/Lime.
Avoid disturbing the roots, if possible, when transplanting, as they resent that and will sulk, by collapsing onto the ground, for days or weeks afterward.
It's difficult to predict the age at which they will begin to set bloom buds, but it is not unreasonable to expect a 2 year old nursery grown plant to produce some blooms.
BTW, the correct botanical name is Helleborus x hybridus.
H. orientalis is a green flowered species and was used as one of the parents to produce the multicolored hybrids we grow today. Some nurseries incorrectly label x hybridus as orientalis.
Enjoy! :Rb

Thanks a lot for the advice, Rb! They will be arriving barerooted, so I need to plant them out in a planter for now. I have potting soil, perlite, peat moss, manure, Maxicrop, seaweed fertilizer, leaf mold, and lime plus stones for good drainage. Any suggestions of what mix to put in the planter? (I'll also surround the planter with mulch and place it against a corner between house and steps for wind protection in a spot that gets some doppled light in the afternoons.)