As for why the Second Hokage had only arrived now, that went back to what happened after Jiraiya found them a few days earlier.
A few days earlier.
Hashirama Senju, Madara Uchiha, Tobirama Senju, and Hiruzen Sarutobi were still immersing themselves in red thought.
While they were diligently attending class, this world's Jiraiya arrived, hoping to bring the First Hokage and the others back.
But before Jiraiya could speak, a look from Madara Uchiha intimidated him into silence.
At that moment, Madara was like the class study monitor.
With a single sentence, Madara could wake Hashirama Senju, who was too drowsy to absorb the lesson, or silence Tobirama Senju and Hiruzen Sarutobi when they whispered to each other.
Naturally, silencing Jiraiya with a single look was no problem either.
Feeling the pressure Six Paths Madara exerted in the classroom, Jiraiya initially planned to ask the group of six from the Otherworld for help...
But after thinking it over carefully, he gave up on that idea.
The reason was simple: he had come to find the First Hokage in hopes of bringing him back to intimidate the Four Great Shinobi Villages into abandoning their attack on Konoha.
With that in mind, he could only sit on the sidelines and listen, waiting until Madara, the study monitor, was absent before approaching the First and Second Hokage...
But what Jiraiya never expected was that, after sitting in on the class for just over ten minutes, he would be drawn in by the lessons on red thought.
He had already heard his Otherworld counterpart explain red thought and revolution, but that had only been a general overview, nowhere near as detailed as Uchiha Itachi's explanation now.
Although Jiraiya was only sitting in on the class, he still received a complete set of