But, in the case of these trees in Australia (tropical part) you can harvest the sap like maple syrup, not wait for seeds. Thus you would be making fuel while waiting for good hybrid seed production...............
If you're testing for YIELD after three years, you must be getting something, though obviously not what you'd get from a mature tree. So, pick out the worst half of the trees, drain them dry then cut them down. If the "diesel" thickens beyond use as fuel, it appears to have some health benefits. I wonder if the lumber's any good.