Read this: https://docs.mendix.com/refguide/datetime-handling-faq
All the dates are stored as UTC in the database.
Regards,
Ronald
[EDIT]
And do note that execute microflow actions do not have a user context and hence no timezone.
executeMicroflowInBackground is running in the system context so will be using UTC for it’s timezone, not your current locale.
This has caught me out in the past, and is a very easy mistake to make.
Good luck!