@Bart: I just submitted  invent.kde.org/education/kstars/-/merge_requests/365 which uses the artificial horizon constraints in scheduling.
If activated, it would delay a job until the target is above the horizon, and stop a job once it falls below the artificial horizon. 
To use it you both need to check a new checkbox and include that with your scheduler job, similar to the way you'd include an altitude constraint, 


and also, you'd need to have at least one activated artificial horizon constraint.


This doesn't completely solve your request, as the scheduler still is picky about changing the order of jobs, but I believe if you put the jobs in the 
right order you could get what you want. I also added a significant amount of testing to the scheduler, invent.kde.org/education/kstars/-/merge_requests/305 so I'm hoping this will open up the possibility for more scheduler changes in the future.

Let me know if you have have the chance to try it out (currently in the beta software--you know you're running it if you see the "Use Artificial Horizon" checkbox on the Scheduler Tab).