I went with 1000BCE to cover the start of foreign rule that Egypt never really got out of. Cutting that off at Persians just seems like a convention borne of Greek histories starting around that time?Considering pyramids were characteristic of the Old Kingdom, I wouldn't consider them particularly salient. I'd mark the end of Ancient Egypt as the end of the Late Period in the mid fourth century, after which Egypt was ruled by a succession of foreign conquerors (the Persians, the Ptolemies, and Rome), although the last few dynasties were ruling a rump state with few accomplishments and little power--but I'd say that's a pretty good example of the crisis system in action (as are all the Egyptian intermediary periods). (We already know the Bronze Age Collapse is referenced in the Antiquity crisis so some anachronism there is fine...)

Either way, the gap is still massive as long as Egyptian "progression" in the game is concerned. It's just one of the facts of life with the 3-age system.