@dawebbreb:
You can disable the sound via Settings->Advanced Settings->SoundSettings.captchasoundenabled
For the script, see here
https://board.jdownloader.org/showthread.php?t=70525
Basically it comes down to an interval script that checks time and then either enable/disable the captchasoundenabled property or silent mode.
Please ask mgpai in that thread for hint/help. He's our script master and I'm sure he will be able to provide a solution to you in no time
To be honest, I would prefer if you could find a solution that fits your needs via Eventscripter, because the scheduler extension is very limited in functionality and I don't see more work *wasted* on it because Eventscripter can achieve so much more