I am looking for help to identify a short story (maybe YA?) featuring time travelers to ancient Egypt. Here's the few details I can recall. (This search obviously did not cover it.)
The short story begins with the protagonist traveling back to ancient Egypt through some sort of a portal arriving in the back road of a busy city. Time traveling seems to be conducted by some sort of agency, sending "historians" back in time to study various historical epochs. It's made clear early on that the portal will open again in a week or two to allow for traveling back to the protagonists original time. Miss that slot and be trapped in the past - that's a key point the rest of the story revolves around. We later learn that our guy was sent back to find out about other time travelers (a man and a woman, I think) that got lost in time. These however worked their way up in the hierarchy, think High Priest or something like that, and have no inclination to go back to the future and thus try to convince the protagonist through various means to stay too.