Well, I did say the sheer scale tends to be the odd feature. In this case, it could have been:

A) built on top of a pre-existing ziggurat-type building - possible, since this happened early in the dynastic era, where Upper Egypt had yet to achieve complete dominance over Lower Egypt, and the pharaoh would have an interest in replacing local religious sites with ones devoted to his own religion. After all, that's what happened to the Sphinx, replacing its original sacred animal head with that of a pharaoh.

B) built using faster transportation means than we give them credit for. Namely, reed boats - reed has insane flotation capabilities, is readily available along the Nile, and would leave no lasting trace after use. Moreover, both reed and limestone get slippery when wet, so a flat causeway (of which there is on-site evidence) kept watered (of which the Egyptians were masters) would provide the perfect path for sliding the blocks to the building sites, boats and all. Now, it would still take a near-constant stream of stone to match that timeline, but then again, the pharaohs were exactly the kind of people capable of organizing logistics like that.

C) built using a combination of the above. Again, the pharaohs had every reason to claim they built the pyramids alone, within their own reign, and it would be easy for them to destroy any records saying otherwise. The actual distinguishing features of the pyramids as such are the cover and capstones - and those can easily fit the given timeframe by themselves.