It would be better to plant directly into the garden rather than disturbing the roots twice needs semi-shade to full shade and a moist humus rich soil.

agree with MG above - hellebores also resent root disturbance, another reason to plant straight into its final position.

If you have just bought the hellebor and it is in a reasonable sized pot, then you could sink the whole pot into the tub whilst it flowers and then plant out properly afterwards. This would not involve disturbing the roots more than necessary.