Engine\Source\Editor\DetailCustomizations\Private\DateTimeStructCustomization.cpp
FDateTimeStructCustomization::ParseDateTimeZone(const FString& DateTimeZoneString, FDateTime& OutDateTime)
In this method, hardcoded timezone. I have no idea why an arbitrary structure is tied to local time.
if you do not use UPROPERTY(BlueprintReadWrite) of this structure, but declare it in c ++, then the DateTimeStructCustomization methods do not work and the structure can be used normally without a timezone.
you just need it not to be configured directly in the editor.
I think this is a BUG.