i found one of the first bits of info about absorbtion - it may sounds like gobbly gook - key point is the that it is Vitd3 dependant
Absorption
About 25 mmol of calcium enters the body in a normal diet. Of this, about 40% (10 mmol) is absorbed in small intestine, and 5 mmol leaves the body in feces, netting 5 mmol of calcium a day.[2]
Calcium is absorbed across the intestinal brush border membrane, passing through ion channels such as TRPV6. Calbindin is a vitamin D-dependent calcium-binding protein inside intestinal epithelial cells which functions together with TRPV6 and calcium pumps (PMCA1) in the basal membrane to actively transport calcium into the body.[3] The active transport occurs primarily in the duodenum when calcium intake is low, and passive paracellular diffusion occurs in the ileum and jejunum, independent of Vitamin D, when calcium intake is high
Discuss your motility time and how this may or may not impact absorption - and based on all the factors, conditions, meds, how many times a day you should split the dosage. My thoughts are, probably about 4 times a day, this will also reduce impact on kidney.