Raise it when the meeting slips out of order, such as debating before a motion is properly before the group, skipping a required vote, or drifting outside the permitted process.
Interrupt promptly and say, “Point of order,” then state the issue in one sentence. The Chair rules immediately.
This is about process, not opinion. Do not use it to disagree with a speaker’s view or to make your own argument. It is strongest when raised right away.