With the JL-Alpha's time machine unable to reach the 853rd century, Superman Secundus is able to punch through the time barrier to bring the Legion back to the 853rd century. They arrive in time for Superman-Prime's arrival and the final destruction of Solaris.
The JL-Alpha's time travel limitations prevent it from reaching the 853rd century, but Superman Secundus is able to bypass this obstacle by using a different approach, bringing the Legion back to the 853rd century in time for Superman-Prime's arrival and the destruction of Solaris.