Reus

This achievement can be unlocked in alt mode and can be stacked with all of the other 1-hour ambassador achievements.

Before loading a game activate all alt mode benefits and make sure to select a large world. You will receive six random ambassadors at the start of the game, make sure you start with two forest ambassadors on the forest giant. This will net you level two plants and level two fruit aspect which you will use to grow Great Pear Trees. You will also want two desert and two swamp ambassadors so you can snag all of the other 1-hour ambassador achievements.

You will be making orchards of Great Pear Trees on forests for this era. I will be describing the desired layout moving clockwise. From the start lay down an ocean followed by a plot of forest twelve tiles in length (you will need to use your ocean giant to trim off one tile on the other end). On the ninth tile from the start (to prevent the village from settling anywhere but in the middle of the forest) get your first pear tree started with a plant upgraded with two fruit aspects. Plant a second pear tree on the tenth tile and move on. Repeat these steps moving clockwise. You should be able to fit seven villages (with the seventh being slightly shy of twelve tiles). Do not bother putting on more than two aspects on a plant yet, you want to quickly settle your villages. Place your swamp and rock giants on either end of the world to quickly deal with any wars that erupt between villages and begin filling all ocean tiles within three spaces of land with mackerel using your ocean giant.

Once you return to your first village, place two more pear trees and move on. Continue repeating this process until all plots are filled. Now fill up any empty aspect slots on your trees with the fruit aspect. Once done, sit back, deal with any wars, and fill up the seas with mackerel. Pause often when you're initially setting up your villages, you want that done as quickly as possible. Time is less of a concern afterwards. Keep an eye on what developments pop up in the last twenty minutes of the era. Destroy any that do not offer any bonuses and get a pear tree in its place. Do not pick up any additional ambassadors!

Using this method I ended the era with 4200 prosperity and unlocked all of the 1-hour ambassador achievements. Good luck!