I give online quizzes. I want the students to only see the correct answers after some date/time and only if they have attempted the quiz. I do not understand how to do this. My configuration looks like this

I thought this would let students see the answers only after Aug 29, 11:30, if they have taken the quiz, but they see them immediately.

Of course, now students can talk to each other and tell each other what the answers are, so this is useless.

How do I restrict the date?