The Dusk/Dawn offsets (Configure KStars/Ekos/Scheduler) work, though I can never remember which way is + vs - for each setting. Check in the scheduler to see what it is currently using at the Twilight checkbox.
Mireia - there is an interacting setting you might have missed. Also in the Ekos/Scheduler settings tab: The 2nd line in Offsets is "Pre-dawn". I do not understand what is the intended purpose, or why the default value is 30minutes. But if you change it to 0 then the times shown for Twilight in the Scheduler itself accurately reflect when a job will start and when it will be stopped for dawn.