Dear Preeti,
Well i can understand your problem.. though in reality this is a challenge for HR whihc gives us a scope to make HR function as a stratgeic function rather than a mere adminsitrative function and i also know that many of our companys have still a traditional apporach toward sHR.Well in this situation you can better arrange for a meeting with your boss and all yopur colleagues and discus the issue.There is no law which would help you other than getting Overtime incase of more work hours ..This can only be sorted out by mutual understanding and discussion ..See my advise is that do not get frusttated ...and nothing happens better you look for other options ....
All the best ..
Anu:-)