The time requirement is 2:30:00 for A-Scenario / 2:00:00 for B-Scenario. Infinite ATM-4 Rocket Launcher: Beat Leon’s story on Hardcore with S+ Rank (doesn’t matter if A or B scenario, either will unlock it).
The time requirement is 3:30:00 for Leon A / Claire A & 3:00:00 for Leon B / Claire B.