I work with audio and music software (in which timing accuracy is a major component). Timing accuracy 20 years ago was generally far, far better than a modern PC. The Atari ST is still the gold standard -- with regard to timing it makes Ableton Live 8 running on OSX look/sound like garbage. Without multitasking, whatever program you were using could prioritize timing over the GUI and other components in a way that a modern name brand OS won't allow
Again, pure speculation here but this may be the case at least to some degree for Win 3.1 because there aren't as many network services and other bells and whistles running in the background. It may even be the case that Win 3.1 doesn't have real multitasking. Maybe someone can chime in on that