Usando OnCalendar=
com qualquer timestamp com sufixo UTC
requer systemd 228 ou mais tarde. Esta funcionalidade foi adicionada no systemd 228.
Do systemd changelog :
CHANGES WITH 228:
...
- Wherever systemd expects a calendar timestamp specification (like in journalctl's --since= and --until= switches) UTC timestamps are now supported. Timestamps suffixed with "UTC" are now considered to be in Universal Time Coordinated instead of the local timezone. Also, timestamps may now optionally be specified with sub-second accuracy. Both of these additions also apply to recurring calendar event specification, such as OnCalendar= in timer units.