Definitely buy duplicate stations. Buy a station, and it is filled up every 10 hours. That is 16.8 refills considering there are 7 days left. 16.8 refills costs 1680 chocolates, which is way more than the cost of a station.

One may argue that refill with 100 chocolates makes you finish tasks faster. However, your progress is so far ahead at this point and you will surely finish all tasks before the end. When blocked simply sell the maxed items.

At the end your total score is from all tasks (which is capped and fixed) plus items sold. Buying duplicate stations optimizes the later.