I followed much the same procedure as that article at Red Rocket but I had 6 clinics, my defence was around 100, I had 9 people (all settlers - no named people- 6 for the clinics, 2 for food and one defence) 10 beds. My food was around 10 and water about the same (just enough to feed) Decorated with rugs, pictures, statues, lights and a TV (cause cat painting alway put a smile on the face!). Power to the building and the 2 missile launchers I had on the top of the gas bay areas. I had a romantic companion (Cait) so I'd get some bonus XP as I built up and defended the place, and for her witty comments.
Once I had the place set up, I stacked the wooden yellow boxes until the settlement bar was full and i got the "cannot build anymore" notice. Then began the waiting, I was at about 60% at the start and I did end up leaving twice early on since it seemed to move more when I was away (probably just because it's time) but once it reached 80% or so I stuck around. I was only attack by raiders once and the rocket launchers took care of business before I could even locate them.
So I'd sit and wait until midnight, once the settlers had gone to bed, I'd go to bed until 8, Up, mill about, talk to a setter or so, maybe farm food, then sit again, and repeat. I'd see the happiness bar go up every 2nd or 3rd day. And finally, while staring into the dark just after midnight, I got the achievement (I was hoping it would happen when I was in my ManCave of a garage, watching TV, but no - so the screen grab the PS4 automatically takes when you get an achievement is a very dark landscape.
The process probably took about 3-4 hours of real time. It was my final achievement, getting the platinum achievement for 100% completion.
