Hi There!
Getting key durations times is a bit tricker online and needs some custom javascript. Here is a demo from myself and Thomas Pronk to help you on your way
run link online-key-lifts [PsychoPy]
code: Rebecca Hirst / online-key-lifts · GitLab
File in case: online-key-lifts.psyexp (18.0 KB)
Essentially we are monitoring for key events on a list of defined keys ( in this case ‘a’, ‘d’ and ‘l’) when the key is lifted you can see the duration time and that is saved to file - so this should be what you can plug in to your experiment.
Hope this helps,
Becca