Here: https://mindworks.org/blog/meditation-research-science-meditation/

Here is a crashourse - read or listen: https://www.insightmeditationcenter.org/books-articles/meditation-instruction/

In my neck of the woods I'd expect learning how to meditate. It takes 1-2 hours.

What's interesting, some Buddhist monasteries in Asia have programs for problem youths where folks have a choice of going to prison or staying with the monastery until the abbot feels they are in a good spot. I remember, usually it's somewhere around 1-6 months. They learn how to meditate and basically leave with monks and follow the same routines and discipline. It's said that the impact is usually hugely positive because children and teens learn how to be mindful that allows them to observe and to manage their negative thoughts, speech and actions. It becomes a life-long thing, just like learning how to ride a bicycle.

I don't know how well this approach scales, though. We would need a lot of those monasteries here in the States.