In the Indian Railways system, which operates the world's most extensive "Sleeper Class" network, the official sleeping hours are regulated by the railway code to ensure fairness among passengers. You are permitted to use the middle and lower berths for sleeping between 10:00 PM and 6:00 AM. Outside of these hours, the middle berth must be folded down, and the lower berth must be used as a shared seating area for all three passengers assigned to that "bay." However, there is a degree of social flexibility; if your fellow passengers agree, you can often start sleeping earlier or stay in bed later, especially on long-distance multi-day journeys. Passengers with the upper berth have the unique advantage of being able to sleep or lie down at any time during the day, as their space does not interfere with the seating below. These rules are strictly enforced by the TTE (Traveling Ticket Examiner) if a dispute arises, as the goal is to balance the "seating" needs of the day with the "sleeping" needs of the night for the hundreds of millions of travelers who use the class every year.