Around three years from seedling to flowering size plant. They probably won't be the same colour as the parent plant.

I too had been wondering the same thing but I have two seedlings that are now in flower and the main plants were planted in March 2012. I had hoped to move them to another location but I think I will leave them where they are as they are obviously happy there.

Moon growe-you've pique'd my curiosity! Why won't they be the same colour? If the mother plant is pink what colour might the flowers be then?

They are hybrids which means that any of the colour plants which provided genes to make the seed parent could show up in the babies.
It is only species which produce identical (as far as any seed grown individual is identical to the parent) offspring.
Indeed that is one of the definitions of a species.
Hellebores grow new roots as the season gets cooler so the best time to move mature plants is from September onwards until the first frosts.

As Owdb. says they are hybrids… You could get some spectacular colours or a muddy mess.