gistfile1.txt

# systemctl is-enabled say-hello.service
disabled

# systemctl is-enabled say-hello.timer
static

# systemctl status say-hello.service
● say-hello.service - Say hello
   Loaded: loaded (/etc/systemd/system/say-hello.service; disabled; vendor preset: disabled)
   Active: active (exited) since Tue 2016-04-19 11:26:21 PDT; 19min ago
 Main PID: 14368 (code=exited, status=0/SUCCESS)

# systemctl status say-hello.timer
● say-hello.timer - Say hello every 3 minutes
   Loaded: loaded (/etc/systemd/system/say-hello.timer; static; vendor preset: disabled)
   Active: active (running) since Tue 2016-04-19 11:40:49 PDT; 5min ago

# systemctl list-timers
NEXT                         LEFT     LAST                         PASSED      UNIT                         ACTIVATES
Wed 2016-04-20 00:00:00 PDT  12h left Tue 2016-04-19 10:42:10 PDT  1h 4min ago logrotate.timer              logrotate.service
Wed 2016-04-20 00:00:00 PDT  12h left Tue 2016-04-19 10:42:10 PDT  1h 4min ago man-db.timer                 man-db.service
Wed 2016-04-20 00:00:00 PDT  12h left Tue 2016-04-19 10:42:10 PDT  1h 4min ago shadow.timer                 shadow.service
Wed 2016-04-20 10:57:17 PDT  23h left Tue 2016-04-19 10:57:17 PDT  49min ago   systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.service
n/a                          n/a      Tue 2016-04-19 11:40:49 PDT  6min ago    say-hello.timer              say-hello.service

say-hello.service

[Unit]
Description=Say hello
After=network.target

[Service]
Type=oneshot
ExecStart=/bin/echo "Hello, World!"
TimeoutSec=0
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

say-hello.timer

[Unit]
Description=Say hello every 3 minutes

[Timer]
OnCalendar=*:0/3:*