So it can be started around the end of 0.38 content and not around step 51 in the walkthrought which hinted at such content being accessible quite early?I ran a test on my "Completes 0.38" save (link in the signature), didn't do any watersport stuff, and it was successful
After watching Janice in the shower 4 time and got spanked once
I was able to peek on Janice on the toilet 3 times before you watersport scene
After which I was able to do the watersport scene at the end of 0.39
I did not attempt peeking on Janice that early and waited till I had affection around 150 or so. Therefore I kinda wondered then if such content might not be accessible/locked if the player does not express interest in it early on or if Janice's affection gets to high for the game to recognize the correct reaction at that time.