Just prior to the execution attempt. The Context: As the executioners raise their swords, they suddenly collapse.
In the chaotic climax of the Marineford Arc, Monkey D. Luffy is far from the refined Haki user he becomes post-timeskip. He has no control over his abilities, and he isn’t even aware of what Haki truly is. Yet, despite his inexperience, Luffy unconsciously uses two forms of Haki during the battle — moments that are easy to miss but deeply significant for the story.
Here is a breakdown of exactly when Luffy used Haki at Marineford and the significance of each instance.
Here’s a well-developed text on the subject: