Keep Your Foot on the Pedrogas
From Halopedia, the Halo wiki
The 3-hour time limit is calculated as the sum of the player's best times on each level on Legendary on either solo or co-op; players can view their best times on their Halo Waypoint service record. As a guide, players should aim for the par times, as they total 2:35.
The achievement's name is a reference to the speedrunner Pedrogas.