Does the game calculate the score BEFORE or AFTER the End-Of-Turn?
IIRC, the in-game score is calculated between turns, and indicated in F8 at the beginning of your turn. If you complete your marketplace between turn T and turn T+1, you'll have all your happy people at the beginning of turn T+1, and it should be reflected in your score on turn T+1.
Bear in mind - your total score is the result of a running average of your individual in-game turn scores...so if you're milking a game the result of those 6 happy citizens for that single turn will not matter much at all. Over the course of 300 turns or so those 6 happy citizens will make a real difference in your overall score (
ceteris paribus). Over the course of 100 turns...less of an impact. Half a dozen happy citizens for a single turn... I'd be surprised if that added a single point to the end-game score at 2050.
Key to maximizing your score is to lock in those points early. Once the game matures it is very difficult to affect the final score. SirPleb came up with a nifty little calculator that will look at the score from the current and previous turn, and calculate an expected score at 2050.
During my last COTM "Milk Run" I actually tracked my in-game score as well as the projected 2050 score from SirPleb's calculator. (If it matters, I think this was the game that got me a cow award...but don't hold me to that.)
If you look at the graph below, the jagged blue line indicates the theoretical maximum score from SirPleb's calculator. The pink line is the in-game score logged each turn.
As you can see from the graph, the theoretical maximum moves a bit based on what happened to my score during each turn. Once you're about 360 or so turns into the game it is very difficult to move that theoretical maximum. By the time you're 100 turns from endgame the theoretical max estimate doesn't fluctuate much at all, and becomes a nearly dead-linear function that converges with the actual score at endgame.
To make a long story short... the timing of the six happy citizens isn't so much a function of whether you get them on turn T or T+1...it matters more if you get them on turn 200 or turn 400. I hope that helps.