It's disabled by default. Some commentary on some news site (sorry, forget which one) suggests that they had originally intended to have it on by default, but decided at last minute against it.
And with good reason.
It's not at all reliable.
It seems to be trained for "traditional" hand-washing. e.g. simple back and forth rubbing. If you go through the whole rigamarole that we all learned from a certain viral video by a Vietnamese boy band early in the pandemic, the timer stops when you are doing the fancy parts. (each finger, then hand clasp).
I guess it's a good thing, because I think the recommendation is 30 seconds not 20 so it ignores the fancy parts and you get 20 seconds of simple back and forth rubbing plus the flourishes.
You can't complete the "boy band hand washing" in 20 seconds!
BTW, I finally got it down good (as well as proper way to put on a mask) after taking a (really) short free Osmosis course. Osmosis is an online learning platform for medical professionals. Covid-19 - What You Need to Know, if anyone is interested. It gives some CME credits useful for medical professionals. I'm not a medical professional, but I went for the certificate anyway. The course is on Coursera. But DON'T sign-up directly on Coursera. You have to go to Osmosis and get a coupon first, and then apply it when you check-out at Coursera and it will be free. (Normally free to audit, and some fee if you want a certificate.)
FWIW, I also have taken the much more extensive Imperial College Covid-19 Coursera course, which is free, but no certificate offered. I really recommend this if you have the time. It was developed as the pandemic played out - an 8-week course, but took them much longer to write the course, it was dribbled out - which was their intent. Because of this, I was a lot less freaked-out than a lot of the people around me, because I knew what to expect. Even though they made some hopeful statements, it was clear to me from the start that we are looking at at least a 2-year process to normality...
The Osmosis course I think would be great for everyone in a clinical practice or really any service job where people interface with the public. Really basic awareness and really precise instructions on mask donning/doffing and hand washing... It is SHORT, 1-2 hours.)
Oh, geez, I think now the handwashing timer is triggering on my typing! I use an old-school clicky keyboard, (Unicomp) maybe somehow it hears it as handwashing!