Again, that does not seem like news. It has long been my understanding (and I claim no expertise on the period) that the invasion was a long drawn out process, perhaps over centuries, certainly many decades. Furthermore, anyone with much clue about how history works would suspect that the Hengist & Horsa story was largely legend (i.e., that although there might have been - probably were - real people and events behind the story, they probably were not as neat and did not have the pivotal importance that a chronicler like Gildas would tend to assign to them, in order to be able to tell a pretty story).