i try to rush myself through the keyholes since Ive gotten good at them because the flattened 3d figures really just drain so much of my time. So, while working very quickly through the problems I still usually only miss 1 or 2 which is more than acceptable to me. The ones I usually miss are when there are 5 nearly identical apertures and the difference between each of them is like a nanometer per line. No point spending a long time on a problem you probably arent going to get right anyhow. For me at least the cube counting and flattened 3d shape problems take a lot of time, but if I spend long enough on them, I get them right. Some of those apertures though you can seriously stare at all day long and still miss it.