Hi Dominik,
Greetings from Syncfusion.
We have checked your requirement of arranging appointments in TimelineView with different vertical start positions. We regret that, as default appointments will be arranged on top and start position cannot be changed, this is the standard followed by outlook like calendars.
In scheduler, you can change height for timeline view appointments using TimelineAppointmentHeight property of TImelineViewSettings class, this will arrange the appointments with specified height but start position will not change.
Please refer our UG documentation to know more about appointment height,
Regards,
Karthik Raja A