You should try creating a cron job with the following command:
service cp restart
That restarts the captive portal daemons (Apache).
It’s a bug into a bug 😀
I discover that if I “Test” it (with the button), it worked.
But the crontab does not inherit the $PATH, so I replaced with absolute path:
# Bash script: RestartCP-Cron
/sbin/service cp restart
Now is ok, I saw it in the logs.