Hello Nana,
I divide my hellebore all the time, they are easier and very similar to dividing Hosta. My only concern would be how hot it will be this summer and what stage the new summer foliage is at.

I would suggest to prepare a planting site and transplant in late August or September.

What USDA Zone are you in?

Bruce

Nana,

I lift and split as the flowers are just going over and before the new leaves are really growing well.
You can see what you're doing and new roots will be forming at ths stage, be careful when lifting to avoid damage where possible to the white new roots.

Do not let the roots dry out.
If splitting split into big chunks with 4-5 eyes in each, hose the excess soil off so you can see what you're doing.
Transplant into a well prepared site and water in well.
Keep them moist not wet this summer and you should have 100% success.

Be warned the root ball on a big plant can be a 2 man lift.

Have a search round this forum, this is a perennial question.

Cheers Greenmanplants