Looking at the Timeline for the Astral Express displayed in the Wiki, made me realize that Himeko travelled for at least 13 Years through the Cosmos, with Pom-Pom as her only companion. Given that there are no other passengers mentioned between the departure of the Astral Express in 1984 of the Arcadian Calender and December 8098 SC. The 13 Years are a rough estimate based on the fact that both the Arcadian and the Star Calender of the Xianzhou use a System of 12 Months per Year. While at the same time assuming that everything since the start of our Journey happened within one year or a little bit more, as the current events happen in 1999 of the Arcadian Calender, while 8100 is the latest year given by the Star Calender to date the current events. Given that Himeko departed on her Journey 15 Years ago (1984 of the Arcadian Calender), this should be 8085 according to the Star Calender by used by the Xianzhou Alliance. All based on the explanation that the Phantasmoon Games happen every 15 Years. I might be Wrong and the Events are shifted by one year. Given that some Events relevant to our Adventure on the Luofu happen in March of 8100 SC and it feels weird to think that the events hsppened within less than 9 Months. According to the Wiki Welt, Void Archives, and Dan Heng boarded the Express sometime during or after December 8098 SC.
"December, 8098 SC — The Xianzhou Yaoqing reports a resounding victory against Asmodeus' abominations.[220]
Sparkle goes to Earth and recruits Vita to the Masked Fools.
A young Clara reactivates Svarog, who begins taking care of her.
Welt and Void Archives board the Astral Express for the first time.
Void Archives repaired "Shush" before he left, with Himeko's last words to him being "shush."[222]
Dan Heng boards the Express after being exiled from the Alliance.
The crew encounters March 7th drifting in space, encased in Six-Phased Ice. After thawing her, she becomes a member of the Astral Express."
The context of these Events gives us one more date: March 7th 8099 SC, the day March 7th joined the Astral Express Crew. Which means the Express grew in strengh extremely fast. I took the Year 8099 SC because otherwise March 7th joining the Express wouls be considered part of the Present events on the given timeline. Anyways that means that, Sunday and the TB aside, the currently known AE crew came together within 4 months. With Himeko and March7th forming their known bond extremely fast. Maybe because March was the first Girl who joined the AE Crew.
"March 7th looks at herself in the mirror, imagining dozens of potential past lives for herself as she tries on the various outfits that Himeko had assembled for her." March 7th, Character Story: Part IV
Afterall Himeko was the one to pick out her outfits. Shown on the description of the light cone "This is Me!"
The girl could rock any outfit she chooses, but she was unsatisfied, judging by the dozen sets of clothing piled up behind her.
"Will this be the last outfit for today?"
She thought silently to herself and looked at the girl in the mirror. She looked extra happy on this day.
With Himeko brushing March7th Hair, she's also the one ask "Will this be the last outfit for today?". Which means Himeko had the greatest Influence on the March 7th we know now.
Now reaching into territory of Headcanon/Assumption, i like the Idea that Himeko was the first one March 7th saw upon being freed from the ice. And thus bonded with to the point of them interacting the most.
Regardless, the Timeline shows that Himeko had to learn act as a Leader, Guide and Parent extremely fast. Even if Welt and Dan Heng were mature enough. Because the Nameless of the Astral Express became a proper faction rather suddenly.