They can go many years without dividing. When you divide them, pay attention to their growth patterns. Many, like my lady, do a substantial amount of leaf growth in autumn. September is an ideal time to divide. Hellebores can also be propagated by seed.
Stored seed can take years to germinate.
Since seed you buy through seed suppliers is always dried and stored, it doesn't germinate well or easily, giving rise to the theory that these plants are hard to grow from seed. Not true, if you have fresh seed. If you have a clump for a few years, you will find many seedlings around it. You can dig and pot or dig and move these easily. This clump grows in almost total shade once the trees and shrubs have leafed out.