My problem are if you log in to the attendance system there is a 30 minutes interval before you can log - out to the system. then if you log- out to the system you can log -in again, until you complete the 8hours of working for one day.

Two things:
1) Title - Time interval....i need an answer pls.. -- i need an answer pls??? Why would you post a question and not expect an answer? Just describe the problem, don't add a useless order to it.
2) Always reread your post to make sure it is understandable. As written it makes no sense. Do you mean:

1) When you log in you have 30 minutes
a) before you can log out (stuck to 30 minutes logged in)
b) then you will be automatically logged out.

2) You cannot log back in for
a) 8 hours.
b) until the next day.