Hands should be washed for 20 seconds, at least. That’s very hard for many adults to time, so it is suggested to sing Good Morning to You (royalty free) or Happy Birthday twice. See previous, Song to time hand washing for hygiene and disease prevention
A young friend of mine and her younger brother helped me record this version of the birthday song in Yup’ik Eskimo. Total playing time is 20 seconds (mp3 file).