Hi Chippy,
There is no such thing as "Work Timings". Its a myth that if you have a 9-5 job then u go to office at 9:00AM and leave office at 5:00PM. Though it is totally on case to case basis, sometimes its that because of the work pressure you HAVE TO stay for longer hours. However if in case you have to stretch just because your supervisor is bullying you, I would say you have to gather courage and stand up from your seat just when the clock hits the time. Just go to him/her and say "Do you have anything for me to do today......because i am leaving for the day". Don't ask, just tell. I have been working with the largest IT company in Asia for about 11 months now and trust me if you have your work up-to-date, just keep that attitude in you & nobody can bully you.
Wish you all the luck for future assignments.
Regards
CA Sheli Sehrawat