The researchers conducted a field experiment to find the best time to harvest winter rape plants. They looked at factors like oil content, seed weight, seed yield, pod ratio, and oil production at different days after flowering. They found that the best time to harvest is around 58 days after flowering, as this is when the plants have the highest oil content and seed weight. Harvesting later than 60 days after flowering can lead to a decrease in seed yield due to an increase in dehiscent pods.