TL;DR
A change is done only after you verify it is live. A commit shows the code changed; it does not prove the change shipped.
what does a commit actually prove?
A commit proves the code changed. It gives you evidence of a change in the repository, but it does not tell you whether that change reached the live site or service.
when can i call a change done?
Call it done only after you have verified the change is live. That check is the receipt that it shipped.
what should i check before saying a change shipped?
Check that the change is live. The commit and the live verification prove different parts of the work, so both matter when you report completion.
Does a commit mean my change is live?
No. A commit proves the code changed. Verify the change is live before saying it shipped.
When is a software change done?
When you have verified the change is live. A commit alone does not establish that.