I don't think you gave the time of your guided tour start. Our first part (Auschwitz) of the tour broke in time to eat something in the cafeteria before meeting our guide at a specific (proprietary) camp transfer bus to Birkenau, where the tour continued. I have to say that (no fault of the guide) much of the tour time was spent walking to and waiting to enter the specific Barracks that were on our tour, I mean like the famous displays of shoes and other items. I say this not to suggest that you are missing anything, but many of the Barracks are set up with displays for visitors from specific countries or (I imagine) ethnic groups. I believe independent entry is NOT allowed to any of the Barracks.
Besides crowds and slow-moving guests, the Barracks are hard to navigate because of the circuitous paths, domestic box fans everywhere (thank goodness!), and less than bright lighting.
Both camps are very big, so the walking is unavoidable. I felt the Birkenau tour was inferior to the Auschwitz tour, and despite having a guidebook, we would have benefited from a parting, "The crematorium is over there, a ten-minute walk, and ... ", which we did not get.
This is not intended as a review or a one-star flame, but only to point out that you need to allocate a lot of time to walk around (and take the bus as much as you want) and see things that are not included on the tour. It is unbelievable how many people go through Auschwitz every day. Obviously you have to know when the last busses and last trains are, for your transit plans. We used Rick's recommended driver service, which was expensive.
We had no interest in the salt mine, and bought (but back then could not download) our Schindler factory tickets well before our vacation departure. There were complex "pickup" options. I would not wait for arrival in the city. BTW, the Schindler Factory is, quantitatively, more about life under the occupation than about the movie's events. Despite limited tickets, it is also crowded.
https://community.ricksteves.com/travel-forum/trip-reports/four-cities-in-poland-2019