Everyone has been advised to wash their hands for at least 20 seconds. A good way to make sure you’re doing it long enough is by singing song lyrics.
I love this hand-washing guide I found on Twitter (you can find the original here and you can make your own here). Below it (and in the link) you will find a video of the music that goes with it, Perotin’s Viderunt omnes (and see why I found it amusing; the page turn just adds to it).
Image attribution: https://twitter.com/DrCanonic/status/1237364191763271680, created using https://washyourlyrics.com.