Thank you both for your answers as these are important aspects.
As for waiting more time, I've tried it, but concluded that even if given all the time to release alone, marks still exist (supposedly in the points were it had difficulty to release).
We rechecked our hand placement, concluding that fingers don't touch the bottom of the mold.
We are testing with cold molds with partial success.
Mold heating seems to be the way to go, but to get the right temperature with a heat gun is not easy and it's time consuming...