When after concussions do brain hemorrhage occur?

Not direct: There is not a direct correlation between concussions and brain hemorrhages. In people sustaining bruising or hemorrhage into the brain with a significant brain injury, the highest risk for expansion is generally within the first 24 to 48 hours.

Extremely rare: You are asking about delayed hemorrhage after mild closed head injury. In a recent study in 2012, in patients on blood thinners or anti-platelet medications, who are at increased risk for bleeding in general, there were 4/687 patients on blood thinners, and zero in other group. In patients not on blood thinners, there are no data, but one can extrapolate. I suspect the risk is close to zero.