When my son speaks of playing sports, I've always told him: playing on the team is great, but aspire to be the guy who owns the team. I've always told my son: most of the guys on the team will end up bankrupt with bum knees, but not the guy who owns that franchise.
The daily mindfulness, consistency, and discipline is ultimately more important than the amount of time. In other words, it’s more about quality than quantity. If you use 15 minutes effectively, you’ll accomplish more than you would be able to with two hours of unfocused, random actions.