Look up (internet) sunset for your date before counting on 5PM and onwards. Also check the cafeteria hours, since you want to allocate your time carefully. We had a full hot meal there, cafeteria style. (We did the regular 3.5 hour tour.) That quick meal was possible because there was a gap between our (first) Auschwitz tour, and meeting the guide at the (proprietary) shuttle bus to Birkenau.
I presume you read this on their site:
• One or two-day study tours (6 hours or 2x3 hours):
Specialist tour of the Auschwitz I and Auschwitz II-Birkenau camps, enhanced with selected national exhibitions, the area of so-called Kanada, and the ruins of gas chambers and crematoria IV and V.
It seems to me that if you are allocating the whole day, you'd take the longer tour. It may take a strong constitution to see so many horrors for a full day. The mention of "national exhibitions" suggests that some of the extra buildings are some of the densely packed barracks that display material most relevant to specific countries or oppressed groups. They can't be entered except with a guide, AFAIR. I would expect a great deal of walking.
I have not read anyone's personal report of the Kanada area. But I think there would be something online. Even on the 3.5 hour tour, you will be shown some behind glass displays of (bulk) confiscated property and personal effects.
https://en.wikipedia.org/wiki/Kanada_warehouses,_Auschwitz
https://community.ricksteves.com/travel-forum/poland/6-hour-one-day-study-tour-at-auschwitz
https://www.tripadvisor.com/ShowTopic-g274772-i961-k14701606-Auschwitz_One_Day_Study_Tour_Question-Krakow_Lesser_Poland_Province_Southern_Poland.html
https://www.youtube.com/watch?v=9sG-SAwHQBg