Is completeing Halo: CEA in 3 hours possible?

Taking into account the long levels and the physics engine that, 9 times out of 10, will be against you especially on the levels where you drive a vehicle.

Any tips?

It is possible to beat it in just over an hour. I would recommend watching some speedrun videos and memorizing the maps. Also only fighting enemies that need to be fought cuts down your time by a lot so skip the huge battles that aren’t necessary.