I see being present/mindful/"in the now" as being focused, and therefore not distracted. Along with that, you are not affected by every input thrust into your path. It may seem counterintuitive, but I think that lends itself very directly towards long term thinking.
Investing by I think most people's definition is focusing on a long term outcome (5 year minimum investing period is a common rule of thumb), and those same people would likely describe day trading and other short term investing more akin to gambling. With that premise, making the best long term decisions would likely be helped by a mindful/present attitude.
That said, you could also argue that being present and mindful would help your day trading as well--but that makes the assumption that day trading "skill" (rather than luck) is a real thing.