Yea, that's Ecstasy. Useful... but also rather weak. Unless it scales a lot with caster skill or with scrolls used at the same time, 'cause the only time I saw one used, on a huge city, resulted in about 500 peasants being born... Which really doesn't cut down the time required for rebuilding by that much.
Depends where you start from. Moving from 3000 to 3500 can be short, but moving from 1 to 501 can be much longer.
