10-20 minutes/day was enough to teach me how to be 'mindful' on demand and mitigated a lot of mild ADHD-type problems in my life (impatience, anger, finding queues unbearable, high sensitivity to noise etc.).
I spent a few months doing more, and it may not be related, but I became increasingly detached from the outside world, more self-absorbed and less motivated. Spent a lot of time just sitting and being content with nothing, which made me question why I should strive for -anything-. Always focused on improving myself, and the way I thought and felt, but it kept me stuck in my own head and not engaged with other people. There is a benefit in doing loving kindness and other forms of meditation that connect you with others.
I spent a few months doing more, and it may not be related, but I became increasingly detached from the outside world, more self-absorbed and less motivated. Spent a lot of time just sitting and being content with nothing, which made me question why I should strive for -anything-. Always focused on improving myself, and the way I thought and felt, but it kept me stuck in my own head and not engaged with other people. There is a benefit in doing loving kindness and other forms of meditation that connect you with others.