Issue Description
As your project progresses you can see a slowdown in your Schedules.
Solution
The first solution could be to simply split your schedules, for example by stories. The larger the project the more complex it becomes with more data needed to be scheduled.
Element Type leaving this set to All Types will mean Archicad has to check all the elements, instead of a select few.
Zones could also play a factor in the time it takes a schedule to rebuild. They are the heaviest elements for schedules to calculate and process due to their connection to many other elements.
Parentheses () Overuse in a single schedule can exacerbate the slowness as it leads to over-checking of elements for Archicad.
Properties if used in the schedule can cause slowness if they have been assigned to multiple classification systems. Make sure to only assign each property the relevant classification to reduce the number of times Archicad has to check