Mendix can do anything Java can do so it is not a technical limitation, rather a design choice of Mendix. You are limited to creating an other scheduled proces/microflow/widget that takes care of the timing.
There is an Appstore Module from mendix labs which allows you to schedule microflows at runtime.
I think it's better to post this is in the Idea forum? Sounds like a design choice to me.
> I have to create a new deployment just to let a scheduled event trigger an hour earlier.
Why don’t you have the scheduled event run every hour. Then at the start of the event microflow compare the time to your constant and decide if it should run or not.