Timers are systemd unit files whose name ends in .timer that control .service files or events. Timers can be used as an alternative to .
Practice
We can enumerate Systemd timers as follow
systemctl list-timers --all
NEXT LEFT LAST PASSED UNIT ACTIVATES
Mon 2019-04-01 02:59:14 CEST 15h left Sun 2019-03-31 10:52:49 CEST 24min ago apt-daily.timer apt-daily.service
Mon 2019-04-01 06:20:40 CEST 19h left Sun 2019-03-31 10:52:49 CEST 24min ago apt-daily-upgrade.timer apt-daily-upgrade.service
Mon 2019-04-01 07:36:10 CEST 20h left Sat 2019-03-09 14:28:25 CET 3 weeks 0 days ago systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.service
3 timers listed.
