Description of problem:

The current timer only is triggered once 6 hours after the unit is activate, not every 6 hours as expected.

Version-Release number of selected component (if applicable):

fetch-crl-3.0.19-6.fc30.noarch

How reproducible:

Always

Steps to Reproduce:
1. Activate the fetch-crt.timer unit
2. After a while things stop working due ot expired CRLs.

Actual results:

Timer run once.

Expected results:

Timer run every 6 hours.

Additional info:

From "man systemd.timer":

Multiple directives may be combined of the same and of different
types. For example, by combining OnBootSec= and OnUnitActiveSec=,
it is possible to define a timer that elapses in regular intervals
and activates a specific service each time.