I did it! I finally finished a speedrun of Nancy Drew: Curse of Blackmoor Manor. About two weeks after my test speedrun.
I actually recorded six different speedruns. With two of them, I made to the end of the game. With the other four, I made big mistakes and had to restart.
The go fish game in the main hall is the hardest for a speedrun, because it takes three and a half minutes to play. If you mess up on that, you've just wasted a good deal of time. Bul is the next hardest thing to do, because you could waste five minutes if you're unlucky and lose it. On the other hand, if you're super lucky, you can beat Bul in about a minute.
Other difficult sections of the game are the frog game in the conservatory, petroglyph punch and Aelous' four winds challenge. They're hard, because their setup is randomized; the pieces are in different places each time. You have to have exceptional bad luck for these minigames to take you a long time, but it's still a possibility.
My second speedrun ended up being an hour, one minute and fifteen seconds. If you don't include the ending cutscenes as part of the game, then the speedrun is a little under an hour.
I am going to post the speedrun on Youtube...eventually. I need to finish the walkthrough for Professor Layton 5 first.