session-timeout for disconnect at fixed time

hi, i want to disconnect user at midnight. So I've read the April 2004's forum and found some solutions. But there isn't anything about where to put Session-Timeout attribute. I've tried to put into users file. DEFAULT Group := 'static', Session-Timeout := `%{expr: ((%l + 86399) %% 86400) - %l}` Service-Type == Framed-User ... It didn't return Session-Timeout. But when I remove Group section from users file then it returns Session-Timeout. Also I've tried to put this into expr section in the radiusd.conf. Then put expr into authorize section. But it says authorize section couldn't read expr. How can I do this? I want to put this attribute into mysql radgroupreply table. What should I enter in the Value field?