You have to survive 3 turns but then you also have to extract. Which basically means 3-6 turns depending on where the evac point chooses to spawn and how many enemies you have to fight to get to it.
I think it tries to spawn somewhat near your soldiers but that might just be down to luck. There’s also been a couple of times where I’ve had to cross the map to get to it.
If it’s not going to spawn next to your soldiers then could we at least get some sort of marker telling us where it’s going to be after the 3 turns are up? That way, if we can’t clear the map and have to hide from the enemy units we can at least move slowly toward the evac point.
I’m also forgetting that I put most points into speed. Basically every point except the ones used to buy class skills. So all my soldiers have a speed of 22-25. With less speed it would take you even more turns to reach the evac.