Sleeping is socially acceptable in public places in Singapore. You see people asleep in all sorts of places - their lunch break at work, in the classroom (students that is), on the buses and trains, even on the footpath! Celia's violin teacher often has to be woken by the receptionist because he is having a wee kip in the next room prior to her lesson.
The work and study ethic is very very strong.. people definitely burn the candle at both ends... and therefore it is understandable that there are a lot of tired people about. Some of Jess and Rhian's class mates will try to set up on-line conferences to discuss school projects right up till midnight. They may have tried this in Alexandra, but not to discuss schoolwork!