Hiro rescuing YT occurs the night he and YT met, 5 weeks prior to Hiro going the The Black Sun, so there is no conflict.
The time sequence of the early portions of Snow Crash is:
- Chapter 1: Hiro receives a pizza with a short delivery timeline
- Chapter 2: Hiro crashes into a pool, meets YT
- Chapter 4: YT delivers the pizza
- Chapter 6: Immediately after delivery, YT is arrested.
- Chapter 10: YT calls Hiro; gets rescued, flees to Hong Kong
- Chapter 12: YT and Hiro are saved by the Rat Thing. YT and Hiro become partners, and YT tells Hiro about Vitaly
Chapter 3: Sometime later ("a few short weeks" after he lost his job as a pizza Deliverator), Hiro lives with Vitaly. He goes to the Metaverse
Chapter 5: In the Metaverse, Hiro heads to the Black Sun - encounters Raven
Chapter 7: In the Black Sun, Hiro sees Juanita, remembers their past
Chapter 8: Hiro talks with Juanita.
Chapter 9: Da5id infected and thrown out of the Black Sun
Chapter 11: Hiro duels in the Black Sun
Chapter 13: Post-duel: in Reality, Hiro heads to a concert with Vitaly; in the Metaverse, Hiro meets the Librarian
Chapter 14: Hiro is still in the library - YT is following the van with Hiro and Vitaly in reality.
Chapter 15: Hiro at the concert (Lagos says Hiro was fired 36 days earlier).
From this point on, YT's and Hiro's chapters are mostly in synch, with Hiro learning about Sumeria, while YT gets employed by the Mafia and Mr. Ng.