Siemens 7LF4 521-0 Operating Instructions Manual page 14

Holiday
After activation the holiday program is executed between 0:00 h on the start date and 24:00 h on the end date (Constant ON/OFF).
After the holiday program has run once, it must be reactivated.
Activating and deactivating grid synchronisation
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Only available in EXPERT mode.
The default setting is PASSIVE. In order to improve
the long-term accuracy, it is advisable to activate
synchronisation if the time switch is supplied from a
on 50/60 Hz grid with frequency adjustment.