+ will have no effect.</para>
+
+ <para>Note that calendar timers might be triggered at unexpected times if the system's realtime clock
+ is not set correctly. Specifically, on systems that lack a battery-buffered Realtime Clock (RTC) it
+ might be wise to enable <filename>systemd-time-wait-sync.service</filename> to ensure the clock is
+ adjusted to a network time source <emphasis>before</emphasis> the timer event is set up. Timer units
+ with at least one <varname>OnCalendar=</varname> expression are automatically ordered after
+ <filename>time-sync.target</filename>, which <filename>systemd-time-wait-sync.service</filename> is
+ ordered before.</para></listitem>