I'm confused -- do you mean "how big will they get" or do you mean "will they continue to grow pitchers as long as they are alive?"

i mean how long will a pitcher forms

My ventrata takes about a month to grow a 4 inch urn. And as it grows new ones, each following urn will be slightly bigger then the last.

For example, the one I bought at Home Depot last year was producing 2 inch urns, This year they are making 4 inches.