Event Merchant's Challenge - Event successfully solved after 3 minutes. You can see the evidence in the clock of Windows' interface (right bottom) and in the text of the event. The event started at 1.00 am GMT+1, and I finished 3 minutes later at 1.03 am GMT+1. You see 1.05 am GMT+1 for reason that I changed the game's language from German to English and started Adobe Photoshop in order to save the Screenshot.
THE SECRET - How to do it so fast?
You only need to exchange bread. You get 6m to 8m bread by each cart and therefor also 6m-8m in points for the challenge/event. I needed only 8 to 10 carts to end the event successfully.