You can set the timezone for scheduled events in the project settings, tab model.
There are 2 timezones for scheduled events, UTC or Server time. The default time zone will be used when you have datetime operations in your scheduled event.
For example in Mendix 3 if you create a microflow which logs the Timezone, the output would be:
If you have a date 01-01-2013 00:00:00 CET and want to do something with that date, for example formatDateTime($Date,'dd-MMM-yyyy') the output would be
Since mendix 4.2 the output would be, if default timezone is CET
There are two timezone settings that influence your scheduled event.
The first is the setting in your project settings, Stephan described this perfectly so I have nothing to add. Just select the exact time zone you want to use in your date formatting and parsing and for the details see Stephans answer.
The second configuration option is the radio button in the scheduled event itself. This influences at what time the event is started. This is either at UTC time or on the local server time.
When using UTC, the server will initiate the scheduled event when the configured time is the exact time in the UTC timezone. The scheduled event always runs at that specific time and this will never change during the year.
When using Server time, the server will initiate the scheduled event when the configured time is the exact time in the server timezone. When the application starts it checks the timezone and uses the server timezone from the server. This should also include daylight saving time in the scheduling. Which means if the selected timezone/locale supports summer time, the schedule should move one hour when daylight saving time is applied.