This is an experiment to see what amount of delay is too annoying for a user to play music.
You can compare this to the similar typing experiment.
By the way: if you're using something like bluetooth headphones, these inherently have an audio delay
(sometimes of as much as 100ms!), so these results will be really personal and aggravating.
Here are some presets:
Type the key corresponding to the piano key you want to play.
If you're not musical, this is Twinkle Twinkle Little Star:
q q t t y y t r r e e w w
This input will help you if you want to use this on mobile: