My Requirement is different:
suppose i am the user named abc.
I login at say 9:15 in the morning. and i open the site www.yahoomail.com
now it should start counting the time . if it is opened for more then 30 minutes. it should be closed.
and if the user try to open it again then it should not open as for the complete day he has used it.( complete day means that in one day he can only open for 30 minutes.)
this is what i want.