‘And Joseph made it a statute concerning the land of Egypt to this day, that Pharaoh should have the fifth. Only the land of the priests alone did not become Pharaoh's.'
The writer summarises the position as it still is in his day. How long the fifth remained the standard we do not know. But when the Hyksos took over things would change. This would suggest he wrote before that time.
But how does this tie in with what we know of conditions in Egypt? Certainly we know that in the period before the Hyksos there was a feudal system whereby the land was largely owned by the nobility with the peasantry under their control. This would clearly be brought to an end by Joseph's reforms, and confirms the picture presented. Assuming, as we have suggested, that this took place before the advent of the Hyksos, their coming would change the situation in the part of Egypt that they controlled. They in fact restored the land to a feudal system.
But when they were expelled and the so-called New Kingdom was established the whole land was expropriated and transferred to Pharaoh, being declared his exclusive property. This may well have been because it was seen as a restoration of the position before the reign of the Hyksos, which would thus confirm the accuracy of the Joseph story. This position then continued for many centuries.