This is about an hour and half into the game if you do absolutely everything, but a speed-run could probably get it in 30 minutes. First, create your character. Soldier is the easiest class, but a good biotic adept will make the game a cakewalk. Each class has strengths and weaknesses.
Spoilers from this point on.
On the ship, head to the back to receive your mission. Land on the planet. You'll lose a teammate. Keep battling forward, but also look around for loot and chances to talk to people. SAVE before you board the train. After that, there will be a timed section where you have to disarm four bombs. One is right after you get off the train. the other three are in each corner of the raised portion. Walk up to the beacon to get this achievement.