Hi Johannes,
I understand that you are trying to set Simulation pacing through a slider in the app.
You can leverage the below commands for the same.
% First enable Simulation Pacing using set_param or simOptions
set_param(model, 'EnablePacing', 'on');
% In the callback function of the slider, retrieve the value of the slider
% and use it to adjust the simulation pacing as per your requirement
set_param(model, 'PacingRate', value); % value is a finite positive integer
Hope this helps!