NPCs don't make it that much harder. Basically, they change your starting frame. Around the daycare, they usually advance it by somewhere around four. So you usually have to try once, see where you landed and then adjust. It just adds a step. However, if I just add 4 to my starting frame and try it from there (ex. pretending your starting frame is 51 instead of 47), I often get it on my first try. Also, everstones make finding your initial frame harder because they make lots of frames look the same.