Is there any specific reason why "monthly" timing isn't presented? A limitation in systemd workings or whatever? I was more feeling like setting the "pkgstats.service" to run once a month, this is how I realized I hadn't created such folder by following the article.
Only modifications -- apart from substituting "weekly" by "monthly" everywhere relevant -- seem to be in the [Timer] section:
[Unit] Description=Monthly Timer [Timer] OnBootSec=20min OnUnitActiveSec=1month Unit=timer-monthly.target [Install] WantedBy=basic.target
[Unit] Description=Monthly Timer Target StopWhenUnneeded=yes
If that seems ok to you I'll add it and update mkdir/systemctl instructions accordingly.