EXO Dynamics Outreach Advocate

Four hours of multiplayer time, cumulative across sessions - no need to do it in one sitting. It comes naturally if you do a co-op evening or two; failing that, an idle session while you each potter about your own base chores counts just fine.

Pair it with the other co-op achievements - 675606844, 771888104 and Interplanetary Road Trip - and a Desolo engine run together, and the timer largely takes care of itself.