[Unit]
Description=Monthly invite to Hackspace's Plenum

[Timer]
# Mondays on 1st to 4th (Thursday would be on 4th to 7th)
OnCalendar=Mon *-*-01..04 15:00

# Mondays that are on the 3 last days of the month (Thursday would be on 1st to 3rd)
OnCalendar=Mon *-*~03 15:00

[Install]
WantedBy=timers.target