for me this is only necessary
in ssh
edit the crontab
crontab -e
and past this rows : (0 min, 9am, all days, all month, only the week)
#Enable Block:
0 9 * * 1-5 sudo sqlite3 /etc/pihole/gravity.db "update 'group' set 'enabled'=1 where name='Enfants_cours';" ; /usr/local/bin/pihole restartdns reload-lists >/dev/null
#Disable Block:
0 18 * * 1-5 sudo sqlite3 /etc/pihole/gravity.db "update 'group' set 'enabled'=0 where name='Enfants_cours';" ; /usr/local/bin/pihole restartdns reload-lists >/dev/null