After logout till 20 mints user can't login.

This is what I understood from your questions.

You wanted to prevent the user to be login for next 20 minutes from when he logs out from the application.

If my understanding is correct, then the solution could be

In user table, you must have record log out time. If not, you should record log out time.
When the user logs in, check the log out time. If it is less than 20 minutes, don't allow the user to login. If it's more than 20 minutes, allow him/her to login.

Hope this answer help you.

Thanks,

Sakthi.