HaloWars Goes Gray is a new flash movie project based in the epic adventures of the Spartan Gray Team who are located behind the Covenant lines to create chaos and break order in the lines.

The timing in the trailer?

Yes the timing of the trailer if you didn't figured out yet is when the Master Chief and Cortana are in High Charity and the Gray team arrives before the M.Chief takes off in the Forerunner structure along with the Prophet of Truth.

Cortana realize it and ask to the gray team to hurry up and reach the M.Chief and assist him to help planet Earth from the invasion of the Covenant.