See the documentation here:
What does the setting Scheduled event time zone do?
A scheduled event also needs a time zone to operate in, just like when a user would run a Microflow you might encounter operations that require a time zone. The setting for Scheduled event time zone defines which time zone this is. Note that this is independent of when a scheduled event is scheduled to RUN, which can be planned at the server’s time or UTC.
My advise would be to calculate the timing of the scheduled events back to UTC and make two scheduledt events where DST comes in to play.
Regards,
Ronald