If you want to verify that it’s running, you could add a second line that is otherwise identical but runs the command
17 */12 * * * touch /tmp/crontab-working
Then a file /tmp/crontab-working should appear in /tmp and should have its modification time updated every day 12:17 and 0:17. That would confirm that the crontab has the general effect that you want.
However, your renewal command is actually wrong as written. It should refer to certbot-auto renew --quiet, not just certbot-auto --quiet.