A clump that I transplanted took two years just to decide if they wanted to live there and finally started sending out runners in the third year. Now they are spreading far and wide, but nothing much happened in the first year or two. Maybe you'll have faster results, but don't give up on them if they take their sweet time like mine did. And make sure the soil stays moist in the meantime.

Lily of the Valley do take a little time to get going. But when they take over - they DO. I believe they spend the first couple of years creating their underground network, and then they pop up all around. I transplanted a few from an area that's filled with them in an attempt to cover an empty patch in a corner, but it took about two years,and they are still not as full as the original area.
Northerner.

Oh, I just wish my Lily of the Valley were not taking over! They must love my yard & garden. I am continually ripping them out from unwanted spots.