meh ... i'm always usually still at uni at like 5-6pm, thats when most of my classes finish. Don't worry, there will still be heaps of people catching the train. Sometimes there are delays (well thats an understatment), if you don't feel like sitting at east richmond, just hope on the train and sit on it while its at richmond. There will always be delays on the richmond line - its the worst line in Sydney.
During daylight saving time its fine, however, when it finishes and your traveling home at 5-6 ... its pitch black outside when your on the train cause theres no major suburbs.
Don't worry though, your pretty much safe on the train, theres nothing to really worry about. Many people start uni at 9am - so they are on the train that gets there just after 8am, then they just leave constantly through out the day.