Scheduled events will only run on server time, or UTC time. All other times are irrelevant. The server time is the timezone where your server is physically located. You will have to set your offset based on these two options.
Servertime is best suited for on-premise servers, since there is no guarantee for servertime in the cloud.
https://docs.mendix.com/refguide/date-and-time-handling#2-relevant-time-zones
[Edit]
In the project settings there is an option to set a scheduled event timezone . This affects time zone-related operations, such as parsing and formatting dates from/to strings and obtaining the beginning of the current day, but not the time of the event itself.