This bug is not the root of the problem.
As Matthew described in his #5 comment, users have to be able to choose the time format. Therefor he filed the new bug, describing the need for a visible switch in system settings.
Until we fix this though, we should follow the per-locale distinction, meaning:
If I am in e.g. the USA, my clock will show either 9:45am or 9:45pm.
If I am in e.g. the UK, my clock will show either 9:45 or 21:45.
This bug is not the root of the problem.
As Matthew described in his #5 comment, users have to be able to choose the time format. Therefor he filed the new bug, describing the need for a visible switch in system settings.
Until we fix this though, we should follow the per-locale distinction, meaning:
If I am in e.g. the USA, my clock will show either 9:45am or 9:45pm.
If I am in e.g. the UK, my clock will show either 9:45 or 21:45.