In the same issue that debuts Bizarro-Lois, Supergirl is told by her mentor, Superman, to practice breaking the time barrier. She races off a hundred years in the future and meets a genius orphan named Tommy. Supergirl saves his adopted parents from disaster and writes about it in her diary once she’s back. It turns out the kid she rescued is the future Tommy Tomorrow of the Planeteers!
This is the moment when it is firmly established that Tommy Tomorrow is part of the mainstream DC continuity. Maybe there was some worry when Supergirl feature displaced Tommy’s feature in Action Comics that readers would not know that his adventures still appear in World’s Finest Comics?