My Kepler Bb humanoids have 2 stomachs for multiple reasons, 1 of which is the digestion of bone.
When it comes to bone digestion, the bone is chewed up and goes through the esophagus into the first stomach. Meat gets digested relatively fast due to stomach acid and gastric proteases. But bone, without the second stomach would stay intact and likely cause bleeding in the small intestine.
However because of there being a second stomach, this changes things. Now volumetric mass density and gravity can both be used to their advantage. Because of the difference in density between partially digested meat and intact bone, the bone will sink further, towards the gastric sphincter. This triggers both the lower esophageal sphincter and the pyloric sphincter to close and the first stomach to push the bone towards the gastric sphincter which then opens to let the bone through into the second stomach.
Here, a higher amount of stomach acid and the presence of bone digesting enzymes both speed up the process. And the fact that digestion in the second stomach is 100% chemical means that the bleeding risk is very close to 0. After the bone is fully digested, peristalsis pushes the digested bone upwards against gravity. So the muscle layer of the second stomach must be thick to provide enough pressure to counteract gravity.
But the digestion of bone still takes a long time. It takes about 8 hours to fully digest an average amount of bone in a meal into minerals, protein, and fat. This is about the timing between the first and third meals assuming hunger is satisfied with every meal. This could mean that the second stomach isn't done digesting bone for longer than the amount of time that a humanoid sleeps.
So how could I speed up this bone digestion further without having to decrease stomach acid pH?