Doing my own research and using Wikipedia, a typical Diesel tree takes 20 years, though in another article it said it was a 15 year investment. That being said, if you start now and keep them in a greenhouse (as they are a tropical plant) at least you could be energy independent in 15 years when you know it will be worse than now. Also the article I am posting below (that others have posted) tells that some trees only gave up 2.5l and some gave 60l, but the average is 40-45l. Something to take into consideration.
So while doing sunflower seed farms for now to keep the oil going, it will be less energy intensive to have trees later on as it takes nothing to tap the tree and filter it, vs using tractors to plant and harvest, then using 4 different machines to hull, crush, filter and finally convert into diesel. While these are small scale, it is added costs that have to be paid back in the money saved by making your own. Whereas, investing now and waiting you just have to push a cart to tap your future oil reserves.
Other places like malaysia and Thailand have been developing these trees for the backwater areas.