So there are 4 different dates that could be used for the final date. First is the date shown after all actions are complete. I think this should be considered the canonical ending night number, since it is easiest to figure out. Next is the number of days taken, which is just n-1, as long as you don’t do anything on the final day. Next, if you time travel back in time by disabling pregnancy, you can remove 124 days from the clock, so n-124. And if you combine both tactics, you get n-125.
Personally, I think the final date without time travel is the easiest to use, but it doesn’t matter as long as people say what number they are using.
I have gotten n=154 (153, 30, or 29). I think this is the minimum nights possible currently. The other people who have lower numbers either have to be missing some actions, or have found some mechanic that I have not.
The theoretical minimum is n=153 (152, 29, or 28). This is because all cumming actions end the night, all actions must be completed once for a 100%, and there are 28 cumming actions. I personally think some people are missing the pregnancy+awake actions.
My speedrun is unoptimal by 1 day. Ideally each day would end with a unique cum action. But very few cum actions are available without getting a bonus or repeating an action. Therefore my first night gets the gentle touches bonus but no unique cum ending. I don’t see a way to optimize this further.