Will is right, its behaving exactly as it should when using max time.
So, when using samples, you have to test. And test, then test some more. You should be able to find out fairly quickly a setting that will work for the majority of your images.
Being a non-european, the decimal/comma thing confuses me, but am I reading that you have to do ten thousand images PER DAY? I'm not even sure how that is possible.
Doing jewelry that in my mind contains lots of reflective metals and refractive gemstones, those are pretty time intensive renders . using the render region window and the HUD (H key) will allow you to box in the most complicated area of your render and watch the samples in the HUD. When the image looks acceptable, note the samples in the HUD and that is a good starting point to do some testing on full images.
And if you are fighting noise in some areas, don't discount the idea of using a denoising plugin in photoshop. There are many that can be automated, I use the Google Nik collection denoiser, and it works pretty good. ITs certainly faster than tripling your samples just to get rid of noise in a small part of the image. Just be aware that being too aggressive with it can take away the sharpness of the rest of the image.
Good luck!