If you take calcium citrate breakfast could be a good option. Between lunch or nighttime I'd say lunch. You should find my calcium suggestions suspicious. I always watch the labs, but place priority on how I feel.
I take 250mg with k2-7 two hours before injecting Forteo, even though I suspect that by pulling calcium from the bones forteo and tymlos summon the osctoclasts and osteoblasts. It's starting to make theoretical sense that the anabolics would work best when taken at night with calcium following in the morning.
It does depend on which type of calcium you take, though.